Meeting 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.

Techno-fixes are pipe dreams in many cases. The real solution is cutting the use of fossil fuels by any means necessary.

Kert Davies research director for Greenpeace

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."

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