The Metro board yesterday took a stand on subsidies that appears to assure that fares will rise in April.

The board declared that its decision last month to defer a fare increase scheduled for January must not result in higher subsidy bills for local governments. Unless Metro meets good fortune in costs or ridership, or cuts service, that will mean higher fares later.

The action came after D.C. and Maryland board members quashed a bid by Virginia to reconsider the deferral of the January rise. Virginia member Joseph Alexander then proposed a motion instructing budget officials to find ways to assure that the jurisdictions will not have to make up the $2 million that will be lost by holding fares steady between January and April. The motion passed without opposition.

State and local governments are already scheduled to pay about $177 million of this year's $339 million operating budget.

The lost fare revenue could be covered in part by using some of the $3 million Metro saved last fiscal year. However, jurisdictions have already assigned those funds to other programs. Or it could be done by cutting service, a distasteful step for any transit system, or by cutting budget "fat."

Rail and bus ridership is behind projections, and fare revenues are now expected to fall as much as $8 million below budget assumptions. Given the size of these shortfalls, the painful step of raising fares seems inevitable. How much they would rise is not clear. But it seems likely that at least a nickel would be added to most base fares, and mileage rates used to compute peak hour fares on the rail system would rise too.

Last month, representatives of D.C. and Maryland, backed by Alexander, who broke ranks with Virginia governments, voted to defer the January rise at least until April on the grounds that it could worsen ridership problems.

The Fairfax County Board of Supervisors, charging that a pledge to raise fares and take the pressure off subsidies had been violated, responded by voting to withhold its subsidy payments to Metro. Alexander said yesterday the county wants a firm commitment that fares will rise in April before it will pay up.

As yesterday's vote reflects, opponents of the January rise, including Alexander, are coming to the view that rising costs will make it impossible to put off an increase past April, regardless of the consequences on ridership. The cost pressure grew almost immediately yesterday as the board approved a $2 million, 6.2 percent cost-of-living increase for its approximately 800 non-union employes. Following past practice, the raise was a weighted average of raises given to employes of area local governments.

Metro also announced the resignation of Metrobus director Thomas Black, who in two years at Metro has implemented major programs aimed at shoring up the troubled fleet. Black said he decided to quit because he had laid foundations for change and could no longer accept the disruption of his family life caused by the job's long hours.

Yesterday, General Manager Richard Page praised Black for working "tirelessly and skillfully" to improve bus service. Both Page and Black denied that he was resigning under pressure.

Black, who had served as head of the bus system in Hampton-Newport News, was among a group of senior managers brought in by Page. During Black's tenure, long-term programs to rebuild buses and tighten maintenance standards were devised and funded by the board. Management of the system's nine garages was decentralized.

Metro officials acknowledge privately that tension existed between Black and some Metro employes who originally worked for D.C. Transit and three other private bus companies Metro took over in 1973. During Black's tenure, garage managers were rotated and he tried to change longstanding methods of maintaining buses, keeping records and dealing with employes.

Replacing Black as acting director will be Shirley DeLibero, now regional director of the three Virginia bus garages. Before coming to Metro in 1981, DeLibero managed maintenance of streetcars on the Boston transit system's Green Line.