The House voted yesterday to provide $237.5 million in federal funds for Metro subway construction in the next fiscal year, 5 percent less than the transit authority had sought to carry out its long-debated plan to expand the rail system to 89.5 miles.

Aides to Rep. Steny H. Hoyer (D-Md.) and Rep. Frank R. Wolf (R-Va.), two Metro advocates, described the measure as a compromise designed to preserve the 89.5-mile plan. A spokeswoman for Hoyer said the allotment was an amount Metro "could live with."

Metro and federal officials are currently engaged in negotiations over a contract aimed at financing the 89.5-mile plan, which includes a Green Line branch to Greenbelt in Prince George's County and a Yellow Line spur to a Van Dorn Street station in Alexandria's West End.

The Reagan administration initially recommended a $250 million appropriation for Metro, an amount in line with the authority's 89.5-mile plan. The House voted to reduce the proposed allotment by $12.5 million.

Congressional aides said it is unclear whether the Senate will seek further cuts in spending for Metro. Under a deficit-reduction plan adopted by Congress last month, most transit systems, including Metro, would face cutbacks of 15 percent.