The House Appropriations Committee voted yesterday to spend $250 million in federal funds for Metro subway construction in the next fiscal year, an amount in line with the transit authority's long-debated plan to expand the rail system to 89.5 miles by the early 1990s.

But congressional and other officials warned that Congress is likely to consider reducing the Metro system's proposed allotment as part of an overall attempt to curb federal deficits.

The Metro funds were included in an $11 billion measure designed to finance the nation's transit systems, highways and other transportation programs. Rep. William Lehman (D-Fla.), transportation subcommittee chairman, said some cuts would be proposed before the bill is considered on the House floor.

Metro officials have contended that any sizable cut in federal spending would jeopardize 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.

Under a deficit-reduction plan adopted by Congress last month, most transit systems, including Metro, would face cutbacks of 15 percent. Metro and other transit officials have urged Congress not to impose the recommended cuts.

Rep. Steny H. Hoyer (D-Md.) and Rep. Frank R. Wolf (R-Va.), two Metro advocates who are members of the Appropriations Committee, met yesterday with top Metro officials in an attempt to devise a strategy to preserve the 89.5-mile plan.

Hoyer said he considers it likely that cuts in Metro spending can be avoided or held to a minimum. A spokesman for Wolf said Wolf also would seek to head off cuts in Metro construction funds.

The current Metro system is 60.5 miles. The 89.5-mile plan is designed to be financed with funds previously authorized by Congress. Metro's long-term proposals call for 103 miles, but no federal funds have been earmarked for the last 13.5 miles.

In a related development yesterday, Metro officials said a planned Red Line extension to Montgomery County's Wheaton station may be delayed by several months until early 1990. Under the authority's current plans, the extension has been scheduled to open in mid-1989.

Officials attributed the postponement to delays in obtaining federal grants and a proposed modification in construction plans. The revised plans would provide for an additional $4 million switch along tracks near Wheaton to allow trains to turn around more quickly for return trips.

In another development, the transit authority announced that the first of 76 Metrobuses withdrawn from service earlier this year because of hazardous cracks in their undercarriages would be returned to operation today.

The controversial buses, manufactured by Neoplan U.S.A. Corp., a West German-affiliated company, have undergone extensive repairs to correct the cracks and other defects. Officials said two more Neoplan buses probably will be restored to service next week. The other 73 are expected to be repaired within the next four months.