The Metro board took a key step yesterday aimed at granting passes to firefighters and plainclothes police officers for free rides on subway trains and buses.

The move would overturn a controversial action by the transit system's board of directors last year, under which the passes were revoked.

The board, acting as a committee of the whole, voted yesterday to reopen the issue by holding a hearing in September. The board would later decide whether to restore the passes.

In another development, a House subcommittee approved a $250 million appropriation for Metro subway construction in the next fiscal year. The proposed spending level is in line with Metro's plan to expand the rail system to 89.5 miles. It is unclear whether the Senate will endorse the measure.

At the same time, the transportation subcommittee of the House Appropriations Committee also adopted an amendment by Rep. Frank R. Wolf (R-Va.) calling for studies of several highway and bridge projects, including an "outer beltway" through Northern Virginia.

The beltway plan, recommended earlier this year by Virginia Highway Commissioner Harold C. King, would provide for construction of an 80-mile bypass around the western edge of the Washington area. The $770 million highway would be aimed at easing traffic congestion on the Capital Beltway.

The Wolf amendment also included studies of a proposed $30 million widening of the heavily congested Theodore Roosevelt Bridge and a new ramp to connect the southbound George Washington Memorial Parkway with the center span of the 14th Street bridge.

Metro now provides free subway and bus trips to uniformed police officers, current and retired Metro employes, and present and former Metro board members. Last year, the transit authority withdrew passes from other government and private employes in an attempt to cut costs and prevent misuse.

The move to restore the passes to firefighters and plainclothes police officers was led by Carlton R. Sickles, chairman of the Metro board's safety subcommittee. Sickles argued that fire and police personnel should be encouraged to use the transit system to help deter crime and ensure saftey in emergencies.