MORE PREDICTABLE than the arrival of a Red Line train from Silver Spring -- and with just as many squeals -- comes local angst in reaction to early reports of the Reagan administration's views on mass transit in general and Metro in particular. Initial word was that the administration wants to slow the pace of Metro subway construction and is studying possible cuts in the planned 101-mile system. Given the long history of White House support for a complete Metro system -- every president from Eisenhower on -- and the exhaustive reviews the construction program has undergone over the years, any hacking off or delaying of planned subway lines could turn out to be as expensive as it would be destructive.

But hold on to those Farecards, because there's still some hope that the "cost-effectiveness" of a full Metro system, built on schedule, is recognized inside the Reagan administration. In remarks yesterday at a session of the National Association of Regional Councils, Transportation Secretary Drew Lewis acknowledged the intense interest of this region in completion of the subway system. While careful to avoid any specific plugs for Metro, Mr. Lewis spoke sympathetically about mass transit projects already under way; systems in progress should be completed, Mr. Lewis said, instead of "strung out" over a period of time. The new transportation secretary also voiced strong support for continuing operating subsidies for mass transportation at least through fiscal year 1982 -- by which time state and local governments could expect to adjust to a cutoff.

Though none of this should be read as an all-points green light for Metro construction, the strong bipartisan interest in completing this model regional mass transit project -- as well as the financial justifications for proceeding on schedule -- apparently have not been lost on the new administration. The last miles of Metro should not be treated as just another "new start" in the national subway construction program. On the contrary, they should be regarded as the logical and financially defensible completion of a sound federal/regional undertaking that has earned -- and deserves -- solid support.