Key members of the House District Committee introduced "compromise" legislation yesterday to transfer the huge St. Elizabeths mental hospital from the federal government to the District government by October 1991, a significant step in the long-running dispute between the two on how it should be done.

"We do have general agreement" between the federal and city governments about the outlines of the compromise, though both do not like parts of it, said D.C. Del. Walter E. Fauntroy. "We have something that can pass muster."

The bill was introduced by committee Chairman Ronald V. Dellums (D-Calif.), Rep. Stewart B. McKinney (R-Conn.), ranking Republican on the committee, and Fauntroy, chairman of the fiscal affairs subcommittee. The subcommittee has scheduled a hearing and legislative markup session on the bill for today.

Under the plan, the District would gradually increase its share of financial responsibility for mental health services in the District over the next six years, while the federal government's share of support for St. Elizabeths would decline each year under a set payment plan.

After September 1991, the federal government no longer would contribute funding to the 127-year-old institution in Southeast Washington.

In the meantime, the mayor would be directed to develop a comprehensive mental health plan for the District, subject to amendment by a specially created nine-member commission.

The federal government would reimburse the District indefinitely for the cost of caring for patients sent to the hospital by federal agencies or courts. There are about 335 such patients out of almost 1,800 inpatients at the hospital currently.

The District would be expected to develop a system that would put more patients into community mental health care facilities, but Fauntroy said there is no way to tell now how many would remain at the institution.

Fauntroy said the committee plans to take the bill to the House floor on Sept. 17. He also said members hope the Senate can approve a measure during this Congress, which is scheduled to end early in October.

Staff aides have said, however, that it is highly unlikely that the Senate can approve something this year, particularly since the Senate committee has not had hearings yet on the St. Elizabeths issue.

Funding for St. Elizabeths has been a long-standing source of controversy between the federal and city governments, and the federal government has been trying to turn the institution over to the city for decades. But the city has not wanted it, saying the District does not need and cannot afford such a large facility.

Congress authorized a special $20 million appropriation for St. Elizabeths for the next fiscal year to avert a possible financial crisis at the hospital, but made it contingent on adoption of a long-range plan for future funding and responsibility at the institution.