The federal government is the nation's largest single energy user and much of that energy is frittered away through wasteful lighting, heating and housing policies, congressional analysts said Tuesday.

The congressional Office of Technology Assessment said the government could save at least 25 percent of $3.5 billion it spends on energy for federal buildings by adopting more efficient technology that would not diminish worker comfort or productivity.By embracing such improvements, the government would not only set a good example for the private sector, but also help the development of new technology by providing a huge market for innovative products, the OTA said.

The OTA noted the government has taken energy efficiency steps since the 1970's and reaped billions of dollars of savings as a result. It said Energy Department statistics showed that, over the period 1975 to 1989, the government invested $2.5 billion in conservation measures and received close to $7 billion in savings in return.

"Despite this achievement, considerably greater savings are still possible," the OTA said in a new report. "Federal agencies' use of many energy efficient measures is low."

For example, it said inefficient, costly-to-operate lighting was still common throughout the 500,000 buildings owned or leased by the government for offices or other uses.

The OTA report, entitled "Energy Efficiency in the Federal Government: Government by Good Example?," comes amid intense debate in Congress over legislation to require increased energy conservation measures in the private sector. Most notably, lawmakers are giving serious consideration to bills that would require automakers to make more fuel-efficient cars.

Within the government, President Bush issued an executive order April 17 ordering federal agencies to reduce energy use wherever possible.

The report was requested by several congressional committees, and lawmakers said the OTA findings made it clear government officials were not practicing the energy efficiency policies they preach.