A General Accounting Office report predicted yesterday that the number of prisoners at the District's Lorton prison will increase significantly during the next several years.

Rep. Stan Parris (R-Va.), who requested the GAO report, noted that the District plans to spend more than $12 million in the next few years to expand Lorton by about 880 spaces to make room for prisoners from the overcrowded D.C. Jail and to increase security.

Parris said he believes the overcrowding and security problems "can best be solved by the construction of a new penal facility in the District of Columbia and by closing Lorton altogether. . ."

The GAO study said that in addition to increases that will be caused by the effort to end the overcrowding at the D. C. Jail, the District's new mandatory sentencing law, which went into effect last month, and a proposal to transfer 150 female prisoners to Lorton, could cause the number of prisoners at Lorton to grow.

The GAO study also questioned arguments by District officials that they must transfer prisoners from the D.C. Jail to Lorton because of a federal court order to alleviate overcrowding at the city jail. The study contended "the court did not specify how the reduction in overcrowding should be accomplished."

Lorton is located in southern Fairfax and is used to house District prisoners.

Northern Virginia politicians and residents have been trying for years to get the facility moved out of the area or scaled down.

About two weeks ago, U.S. District Court Judge William B. Bryant threatened to hold Mayor Marion Barry and other city officials in contempt if overcrowding at the jail was not eliminated.

Parris asked the GAO to identify which expenditures were not required by the court order on overcrowding. The GAO found that two projects fell into this category--the conversion of a minimum security facility to a medium security facility at a cost of $1.7 million and the construction of a new minimum security facility at $5.2 million. Parris has said that the money saved by eliminating unnecessary projects could be used to build a new prison facility in the District.

In another development, D. C. and Fairfax County officials appeared yesterday to be nearing agreement to close down the existing firing range at Lorton and move it to a new site at the reformatory.

Earlier this week, D. C. officials balked at signing a tentative agreement with the county that would have closed the existing range, according to county government sources, and the county was preparing to move ahead with its lawsuit seeking a court order to shut down the range. Agreement between the two governments would keep the matter out of court.

Under the agreement the city would close down the existing firing range if the county would help provide the manpower and equipment needed to build a new range at a different site on the reformatory grounds. But sources said city officials had asked for a more detailed accounting of how the county plans to assist in the job of constructing the new range.

County Executive J. Hamilton Lambert said, however, that requests from some city officials for a more detailed accounting of the county's contributions will not jeopardize the agreement or force the two governments back into court.

Lambert said the issue was raised by city officials "not at the higher levels" who apparently "felt we weren't going to stick to our word." He said he believes discussions between his office and high-ranking city officials Wednesday put "everything back on track."