The General Accounting Office has a suggestion for alleviating overcrowding in federal prisons: give each inmate a roommate.

The Bureau of Prisons would not need hundreds of millions of dollars for "the most extensive and costly expansion program in its history" if federal prisoners were housed two to a cell, the congressional investigative agency said in a report released Tuesday.The GAO questioned the Bureau of Prisons' claim that its facilities were 60 percent overcrowded with 37,421 inmates as of January this year.

The determination was made on the basis of providing each inmate with his or her own cell of roughly 65 square feet, where in practice prisoners have doubled up in cells in the 50- to 70-square-foot range, the report said.

"Despite operating at 60 percent over rated capacity, (the bureau) has not experienced unmanageable problems," it said.

The bureau asked Congress to appropriate $315 million for expansion in the year that begins Oct. 1, reflecting plans to increase its capacity to 74,614 inmates by the end of 1995.

"Costs could reach $2.9 billion by fiscal year 1995 and substantially more if additional expansion is approved to accommodate the 125,478 inmates (the bureau) projects for 1999," the GAO said. "In reality, these expenditures represent only a down payment on the ultimate cost of expansion."

The report was sent to Sen. Sam Nunn, D-Ga., chairman of the Senate Permanent Subcommittee on Investigations, and Rep. Charles B. Rangel, D-N.Y., chairman of the House Select Committee on Narcotics.

"We need to rethink the definition of overcrowding and to commit additional time and effort to analyze our prison needs for the future," Nunn said in a statement.

The prison bureau "could save substantial construction and operating costs by using a double-bunking standard to measure the rated capacity of all new and existing facilities," the GAO said.