U.S. Transportation Secretary Drew Lewis has cleared the way for Congress to give Metro an additional $1.7 billion in subway construction funds in coming years.

Lewis ruled that area governments have set up "stable and reliable" sources of revenue for Metro's operating deficits and debt service bills, thereby meeting conditions Congress laid down for release of capital funds authorized by the so-called Stark-Harris Act of 1980.

Lewis' move will not end the transit system's perennial battle for funding on Capitol Hill, however, because Congress must determine precise amounts to be spent each year. This year's fight is already under way.

The White House has proposed a $295 million capital program for fiscal 1983, consisting of $250 million in Stark-Harris funds and $45 million in highway trade-ins. But a House subcommittee has marked the Stark-Harris portion down to $230 million.

Both plans fall well below the $375 million that Metro's own construction program assumes in both types of funds for fiscal '83. Such a cut would further delay work on unbuilt segments of the planned 101-mile rail system and raise new fears that some parts will not be built at all. Currently 39 miles of track are in operation.

The Stark-Harris bill was passed to create a new "pot" of money for Metro subway construction, as the prime source of recent years -- funds diverted from canceled interstate highways -- runs out. Federal grants cover about 80 percent of Metro's construction costs.

But due to congressional concern that the money would be wasted if Metro were bankrupted by operating deficits, the bill contained a requirement for "stable and reliable" funding sources for operating and debt service costs before any of the capital funds could be doled out.

Metro's ability to pay for itself has been steadily eroded in recent years, to the point that this year fares and other revenues will cover less than half of its $337 million operating budget. Since the Stark-Harris bill became law in January 1980, area governments have passed measures intended to assure federal officials that deficits will always be met.

In Washington, the City Council passed legislation reserving for Metro revenues from the city gasoline tax, parking meters, vehicle registration charges and other fees. The revenues are expected to cover 100 percent of the city's share of operating and capital budgets.

A 2 percent gas tax dedicated to Metro was imposed in Northern Virginia and the state provided $42 million for transit projects over two years. Local governments passed resolutions promising to dip into their general funds for whatever costs remained.

In Maryland, the state agreed to pay 75 percent of Montgomery and Prince George's counties' shares of operating subsidies and 100 percent of their capital costs. The two counties, meanwhile, undertook to make up the rest of the costs.

In wording these measures, area legislators were hampered by the federal law's vague descriptions of what would qualify as "stable and reliable." Though area transit officials were concerned that Virginia's steps might not meet approval, Secretary Lewis has now formally ruled that all jurisdictions have met the standards.