The United States could cut 35 percent of its carbon dioxide output in 25 years without "major technological breakthroughs" or huge energy taxes, the Office of Technology Assessment said yesterday.

But the congressional research agency was unable to pinpoint the costs of such measures to curb the emissions of carbon dioxide, the principal warming gas produced by burning fossil fuels. Cost estimates ranged from a net annual savings of $20 billion to a loss of $150 billion a year, or 1.8 percent of national income.

In the first official comprehensive guide to a potential strategy for combating global warming, the OTA outlined a regimen seeking greater energy efficiency in everything from cars to buildings, forest expansion and reduced reliance on coal by electric utilities.

Even at the highest cost, the large carbon dioxide reduction said to be possible without radical shifts in the economy is certain to influence the debate of representatives of 130 nations now meeting near Washington to ponder responses to the global warming threat.

"While difficult to achieve, major technological breakthroughs are not needed," the OTA said. "Existing equipment would not have to be instantly scrapped and replaced with untested prototypes. The requisite energy-related technologies are either already available or demonstrated and close to commercialization."

Most economic analyses forecast the impact of energy taxes to discourage use of fossil fuels -- chiefly coal and oil -- so carbon dioxide can be cut 20 percent by 2020, the goal of several European nations. Cost estimates run from 1 percent to 5 percent of national income.

The OTA study, however, takes an engineering approach. One set of efficiency and conservation measures is laid out for a "moderate scenario" in which carbon dioxide emissions are held to a 22 percent increase, less than half the amount projected in an economy without controls.

The "moderate" program would result in net savings by decreasing energy demand, the OTA concluded. But to cut carbon dioxide to levels thought necessary to slow down the warming trend, the OTA developed a "tough scenario." The plan calls for an ambitious agenda in which new homes are so well insulated that they would require 85 percent less heat and 45 percent less air conditioning. Also more efficient lighting would cut energy needs of commercial buildings 60 percent, and new cars would get an average of 58 miles per gallon of gasoline.

Utilities would lessen dependence on coal, now used to generate half the nation's electricity, by increasing use of natural gas and new designs for nuclear power plants considered to be safer.

The plan calls for increasing productivity of and planting new forests, which serve as "sinks" to absorb carbon dioxide.