The nation's largest consumer of energy, the federal government, is adding millions of dollars to its energy bills by dismantling programs designed to save energy, according to a congressional study.

The government spent $12.5 billion on energy in the last fiscal year, nearly 2 percent of the entire federal budget, the study found. Energy consumption was up 3.4 percent over the previous year.

Rep. John D. Dingell (D-Mich.), chairman of the House Energy and Commerce Committee, said its oversight subcommittee concluded that "increases in this enormous energy bill can be restrained and millions of dollars in cost savings can be achieved through the implementation of aggressive energy conservation actions and improved management practices."

While federal energy expenditures are increasing, the administration is sending out signals that conservation is a low priority, the report said. For instance, in February, 1981, President Reagan rescinded regulations that restricted temperatures in both private and federal buildings.

The Office of Management and Budget is now drafting an executive order to eliminate other energy conservation measures, including conservation goals for federal buildings. OMB analysts have apparently responded to complaints from federal agencies that the goals were arbitrary. An OMB spokesman would not comment on the proposals.

The subcommittee report projects federal energy expenditures--82 percent of which are attributed to the Defense Department--escalating to more than $20 billion by 1985 unless more progress is made in energy conservation.

Dingell noted that a 1981 Defense Audit Service report concluded that "several million dollars could be saved annually in the Defense Department alone simply by reducing water heater temperature settings in military family housing."

OMB has adopted the position that market forces and budget restrictions will provide sufficient incentive to federal agencies to cut energy use without extensive internal oversight. OMB Director David A. Stockman said as much to the oversight subcommittee in a letter last March.

"Our position was that it wasn't very productive to give the Department of Energy a major role in this area of trying to tell the rest of the government how to save energy," said OMB spokesman Ed Dale.