President Reagan's cuts in programs to conserve energy will do some damage to the agencies that have been trying, without much success, to shave the nation's largest energy bill: the federal government's.

Reagan's budget-cutters all but zeroed out several conservation promotion agencies and programs of the Carter administration, arguing that high energy prices alone have already led to unprecedented energy savings nationwide.

But those savings haven't been very dramatic within the government, where total oil-equivalent energy use was 294 million barrels last year and cost taxpayers $8.9 billion. That is only 6.4 percent less than the 1975 level of 314.2 million barrels of oil, well below the 14 percent savings that private industry has achieved since then, according to the National Association of Manufacturers.

It is also below the rate that oil imports have fallen off in the same period and well behind schedule toward former president Carter's 10-year goal for cooling of federal fires. He called for a 20 percent cut in energy use in existing federal buildings from the 1975 level, a 30 percent drop in use of oil-based fuels and a 45 percent reduction in energy use in new buildings. Only the General Services Administration's 8,000 buildings are even close: down 9.4 percent.

But the GSA, which owns and operates most federal office buildings, consumes only 5 percent of the total energy used in federal buildings, and only 2.5 percent of total energy consumption. The lion's share of federal energy expenses -- more than 81 percent -- belong to the Defense Department, with the largest chunk of money going for jet fuel.

Every time the price of a gallon of oil rises by a penny, the federal energy bill goes up $80 million, according to the Energy Department's Federal Energy Management Program. And despite that 6 percent cut in consumption since 1975, that energy bill has doubled since then.

"We figure we're rougly halfway through and halfway there," said Jack Holton, GSA's energy conservation division coordinator, of the drive to meet the Carter goal.

GSA's efforts have saved taxpayers $70 million, he said. But Holton's office has had its staff cut from 16 people to 12, with the four going to outlying areas. The budget remains intact at $1.5 million. "It will make life a little more difficult, yes," Holton said.

He will cut back some "employe awareness" programs that got everyone to turn off lights and dial down the thermostat, and will curtail answering questions from outside GSA, he said. Instead GSA will concentrate on insulating, caulking and otherwise rehabilitating its buildings, "things that seem to be more important for the program," Holton said.

Jack Vitullo, project manager for the Federal Energy Management Program, calls progress toward conservation "not dramatic, but significant." His office keeps track of everything from Defense Department jet and tank fuel to the heating bill in a Wyoming post office, and its budget has been cut from $1 million under Carter to $530 million.

"It's not as bad as it sounds, but it could be better," Vitullo said. He also plans to cut planning sessions technical guidance programs and seminars, and to defer issuing guidelines and regular reports.

"We would hope we've moved people by now in such a way that they're self-generating," he said, "but we'd just be giving them a little additional emphasis."

Vitello noted that the easiest energy savings took place right after the first oil import embargo in 1973, when gross waste was curtailed. Counting from then, Vitello said, instead of from 1975, total energy use has dropped more than 20 percent. "People really have to work at it now," be said.