ith people crowding the sidewalks and music from clubs and cars in the air, it was the kind of summer night in Greenwich Village when energy seems to emanate from the pavement. Joseph Edmonds, in a dark baseball cap and a white polo shirt, might have been looking for the right nightclub. Instead, he was studying the rows of parked cars.

Halfway down the block from a busy corner, he spotted one that towered above the others, its shiny gray paint reflecting light from the streetlamp overhead. "I'm going to get that Excursion down there," he told Renée Benson, a young woman who was scanning the curbsides with him.

"Please do," she replied.

He walked to the car and, from a stack in his hand, took out a card colored the bright orange of a New York City parking ticket and imprinted with the word "violation." He slipped it under the windshield wiper.

The owner of the car was in for a bout of that stomach-dropping feeling that accompanies the discovery of a ticket. But Mr. Edmonds and Ms. Benson, friends in their 20's, are not with the Police Department. The card was a message from people who hate sport utility vehicles, and the "violation" was owning one.

"Did you get excited when you saw that ad for an S.U.V. in the remote wilderness?" the text on the fake ticket read. "Did you want to sue the manufacturer for false advertising when you started driving it to the shopping center instead?" It went on — at some length — to castigate S.U.V.'s for their gasoholic tendencies and S.U.V. drivers for buying them.

"Think about it!" the flier said. "Why do you need such a HUGE car? This is not a militarized zone!" It accused the driver of "polluting more than your fair share."

Challenging the owners of S.U.V.'s isn't new. In Manhattan, vigilantes have been putting crude fliers trumpeting accusations like "Your car is a killer" on S.U.V.'s for at least two years, and in Brooklyn, a magazine editor organized a protest in which a number of "No S.U.V. Parking" signs were placed on a street last December.

But the phenomenon appears to be growing in size and intensity. Mr. Edmonds and Ms. Benson were working with Earth on Empty, a group concerned about air pollution and global warming that has begun distributing professionally designed and mass-produced ticket look-alikes in a score of states.

Trying a different tactic, two women let the air out of the tires of S.U.V.'s parked at Johnson Ford, a dealership in Kingston, N.Y., last year. This month the were sentenced to 50 hours each of community service.

"There are many of us at the dealership who are environmentally aware," said Vincent Martello, the marketing manager of the Johnson Auto Group, which owns the dealership. "I just think that the strategy that they chose was not an effective one."

Some responses to anti-S.U.V. activism are less restrained. In Greenwich Village, Mr. Edmonds and Ms. Benson didn't wait around to see their victims' reactions, but it's a safe bet they were not warm ones. What the protesters see as activism looks to some on the receiving end like harassment.

"We get really, really nasty e-mails all the time," said John, a founder of Earth on Empty who monitors messages to the group's Web site, www.earthonempty .com. The Web address is printed plainly on the phony tickets.

John, who lives in Cambridge, Mass., would give only his first name because, he said, he has been receiving hostile phone calls from people who have somehow found out about his anti-S.U.V. work. But he did share a sampling of the e-mail messages. In just a dozen of them, S.U.V. proponents called Earth on Empty members tree-huggers, time-wasters, socialists, elitists, litterers, blue-collar workers, freedom-removers, leftists, losers, homosexuals, Democrats and filthy people. And those were the printable epithets.

John himself once met an S.U.V. owner face to face while he was ticketing. The owner and his girlfriend were inside, but not visible from a distance. The owner got out and chased John away from the car, shouting profanities. The group advises its helpers not to give out the tickets before 10 p.m. and not to confront drivers.

The sneak-and-strike policy may be prudent, but it leaves some of the S.U.V. owners incensed. "I don't want to say it's cowardly, but it's leaving something and running," said Darren Thayer, 29, whose Ford Explorer was ticketed in Cape Elizabeth, Me., on Aug. 3.

Christina Allen, 18, who was with her boyfriend when his '88 Jeep Cherokee was ticketed this month in a Wal-Mart parking lot in Eagan, Minn., said they both thought at first that the flier was a real parking ticket. "Once we figured out what it was," she said, "we were really mad."

The thrust of the Earth on Empty message is about fuel economy. But some of the ticketers have other concerns. Candice Manson, 23, another New York activist, hates being trapped behind outsize cars when she's on the road herself. "When you're stuck in traffic behind an S.U.V.," she said, "you don't know why you're stuck in traffic."

John, who runs the Earth on Empty Web site, says the group wants to stigmatize S.U.V. owners the way militant animal lovers have stigmatized women who wear fur coats.

In Greenwich Village, Ms. Benson and Mr. Edmonds cast their net widely; they ticketed a Toyota RAV4, a small S.U.V. that gets 22 to 31 miles per gallon. But Earth on Empty officially advises "Go for the monsters!"

It hands out a guide listing 14 of the "hugest S.U.V.'s": the Cadillac Escalade, GMC Denali, Land Rover Range Rover, Ford Excursion and Expedition, Toyota Land Cruiser and Sequoia, Lincoln Navigator, Mercedes M-Class, Dodge Durango, Chevrolet Tahoe and Suburban, Mercury Mountaineer and Lexus LS 470.

In general, the ticketers are proudest when they snag the big fish. "I like the Excursions because they're so huge for no reason," Mr. Edmonds said. And when Ms. Manson spotted a stretch limousine made from a Navigator, she gave it two tickets.

The stretch may be hard to justify, but many drivers who send e-mail messages to Earth on Empty's Web site are quick to defend their S.U.V.'s.

"We are a family of six with three dogs, often driving eight," one wrote. "What else should we drive? Three cars?"

Another wrote, "We have a home in the country, and the dirt roads can be hard to drive on, especially in the winter and mud season."

One man told a sobering story. "You have no idea why I drive the vehicle I have," his message said. "Maybe, just maybe, it's because my wife and myself have lost a son in an accident and want my family to be safe. Try losing a child."

But in at least one case, an Earth on Empty flier brought about a conversion. Janice Gilmer, 50, a massage therapist from the Upper West Side, said that when she read the fake ticket left on her Nissan Pathfinder, she had a moment of epiphany.

"I never would have bought my S.U.V. if I had any idea about the pollution and the waste of gas and unnecessary size and strength of it," she said. "I've never put it in four-wheel-drive once."

eeting the world's rising energy needs without increasing global warming will require a research effort as ambitious as the Apollo project to put a man on the moon, a diverse group of scientists and engineers is reporting today.

To supply energy needs 50 years from now without further influencing the climate, up to three times the total amount of energy now generated using coal, oil, and other fossil fuels will have to be produced using methods that generate no heat-trapping greenhouse gases, the scientists said in today's issue of the journal Science. In addition, they said, the use of fossil fuels will have to decline, and to achieve these goals research will have to begin immediately.

Without prompt action, the atmosphere's concentration of greenhouse gases, mainly carbon dioxide from burning fossil fuels, is expected to double from pre-industrial levels by the end of this century, the scientists said.

"A broad range of intensive research and development is urgently needed to produce technological options that can allow both climate stabilization and economic development,"the team said.

The researchers called for intensive new efforts to improve existing technologies and develop others like fusion reactors or space-based solar power plants. They did not estimate how much such a research effort would cost, but it is considered likely to run into tens of billions of dollars in government and private funds.

The researchers, a team of 18 scientists from an array of academic, federal, and private research centers, said many options should be explored because some were bound to fail and success, somewhere, was essential.

The researchers all work at institutions that might themselves benefit from increased energy research spending, but other experts not involved in the work said the new analysis was an important, and sobering, refinement of earlier projections.

As they now exist, most energy technologies, the scientists said, "have severe deficiencies." Solar panels, new nuclear power options, windmills, filters for fossil fuel emissions and other options are either inadequate or require vastly more research and development than is currently planned in the United States or elsewhere, they said.

The assessment contrasts with an analysis of climate-friendly energy options made last year by the Intergovernmental Panel on Climate Change, an international panel of experts that works under United Nations auspices. That analysis concluded that existing technologies, diligently applied, would solve much of the problem.

One author of the new analysis, Dr. Haroon S. Kheshgi, is a chemical engineer for Exxon Mobil , whose primary focus remains oil, which along with coal generates most of the carbon dioxide accumulating in the air from human activities.

Still, Dr. Kheshgi said on Thursday that "climate change is a serious risk" requiring a shift away from fossil fuels. "You need a quantum jump in technology," he said. "What we're talking about here is a 50- to 100-year time scale."

Dr. Martin I. Hoffert, the lead author and a New York University physics professor, said he was convinced the technological hurdles could be overcome, but worried that the public and elected officials may not see the urgency.

In interviews, several of the authors and other experts said there were few signs that major industrial nations were ready to engage in an ambitious quest for clean energy.

Prof. Richard L. Schmalensee, a climate-policy expert and the dean of the Massachusetts Institute of Technology Sloan School of Management, said the issue of climate change remained too complex and contentious to generate the requisite focus. "There is no substitute for political will," he said.

The Bush administration has resisted sharp shifts in energy policy while Europe and Japan have accepted a climate treaty, the Kyoto Protocol, that includes binding deadlines for modest cuts in gas emissions. At international climate talks that end today in New Delhi, leaders of developing countries rejected limits on their fast-growing use of fossil fuels, saying rich countries should act first.

President Bush has called for more research, led by the Energy Department, on many of the technologies examined in the new analysis. But some energy and climate experts said the extent of the challenge would likely require far more focus and money than now exists.

Among the possibilities are space-based arrays of solar panels that might beam energy to earth using microwaves. The panel described various nuclear options, including the still-distant fusion option and new designs for fission-based power plants that might overcome limits on uranium and other fuels.

Planting forests, which absorb carbon dioxide, cannot possibly keep up with the anticipated growth in energy use as developing countries become industrialized and as global population rises toward nine billion or more, the panel said.

Some environmental campaigners criticized the study's focus on still-distant technologies, saying it could distract from the need to do what is possible now to reduce emissions of warming gases.

"Techno-fixes are pipe dreams in many cases," said Kert Davies, research director for Greenpeace, which has been conducting a broad campaign against Exxon Mobil. "The real solution," he said, "is cutting the use of fossil fuels by any means necessary."