THOUGH IT HARDLY squares with what people have been hearing for so many years, Metro officials now say they may finish building the subway system almost a year earlier than they last were saying. Quite aside from the pleasant-surprise aspect of this proposition, it makes some financial sense -- which is why Metro's general manager, Richard S. Page, is proposing the speedup. the idea is to make the most of a flat amount of federal money just authorized for Metro, by spending more of it faster and thus trying to get a slight jump on inflation.

By "front-loading" the spending schedule, officials hope to keep down the dollar costs of construction and finish building the 101-mile system in 1989 instead of 1990. local governments have yet to consider how they would meet the $1-for-every-$4 match of federal money. But the proposals offer some appealing changes for various parts of the region.

There would be no revisions in the timing of the first 60 miles, 33 of which are already in use. That means extension of the line from the Stadium-Armory station to Addison Road would still be set for late this year, followed next year by the Red Line extension from Dupont Circle to Van Ness Centre and on out to Shady Grove Road in 1983. It also includes opening of the Huntington extension of the Blue Line from National Airport early in 1982.

Under the new schedule, the Potomac River crossing between the Pentagon and L'Enfant Plaza would be opened late in 1982, as previously planned. The line from Ballston to Vienna would open in late 1984, six months earlier than planned. Tracks from Gallery Place through Southwest Washington toAnacostia would open in the fall of 1985, as set. the Franconia/Springfield extension from Alexandria would open in mid-1986, a year earlier, and the Glenmont line from Silver Spring would open in mid-1986, a few months earlier than scheduled. The line from Anacostia to Rosecroft Raceway would open in the spring of 1987, a few months later than scheduled; the route from Fort Totten to Greenbelt would open in mid-1988, about a year earlier than scheduled; and the last leg of the line from Gallery Place to Fort Totten would open in mid-1989, as scheduled.

Any schedules set by Metro are subject to delays from work stoppages, weather and other unpredictable events. But from the standpoint of riders as well as taxpayers, the sooner the system is built, the better.