You can have wave goodbye to hopes for any second thoughts within the Reagan administration about cutting off federal funds for Metrorail construction. When it comes to intramural sparring between the transportation people and the budgeteers these days, there's no contest; the Office of Management and Budget wins by forfeit. And so it is in these early elimination rounds of the First Annual Gramm-Rudman Games: the White House's dollar figure for Metro in the coming fiscal year still stands at zero -- which matches the influence of the Department of Transporta- tion in this important matter. Even bigger losers are the residents of the capital city's low-income neighborhoods, who have been waiting since the beginning of Metrorail for completion of the Green Line.

It will be up to responsible members of Congress to recognize the fiscal folly of wrecking or stalling the completion of Metro's full 103-mile regional system. At the same time, the challenge to all participating state and local governments will be to resist the kind of infighting that can occur when the money gets tight. Besides, there is an immediate matter that needs ironing out with President Reagan's mass transit chief, Ralph L. Stanley. He's holding back money appropriated for last year and this current year -- with cryptic references to additional conditions that he says Metro should have to meet before getting these overdue -- and urgently needed -- payments.

At Metro's annual conference here last week, Mr. Stanley said it could take several months for a review, reconsideration or whatever it is his agency purports to be doing before it lets go of the appropriated money. His most charitable protion? "I give you my word we're not going to unduly hold up" these payments. The catch word, of course, is "unduly." This money should have been delivered long ago -- and no bureaucratic mumbo- jumbo should obscure the fact that Metro has negotiated patiently and in good faith for its due.