AS LONG AS National Airport is going to be this community's main air terminal, the policy proposed for it Friday by Secretary of Transportation Neil Goldschmidt is a good one. It offers some relief from the airplane noise that now spoils the waterfronts, and it attempts to limit the number of passengers using the airport. But the relief is not as much as the community should have, and the proposed limit on passengers is not low enough.

Underlying Mr. Goldschmidt's proposal is the view that for at least the next decade National will continue to handle more air travelers than Dulles and Baltimore-Washington combined. That is, no doubt, in line with the preferences of those who travel by air, most of whom prefer National to the other airports because of its proximity to downtown. But is not encouraging to those who believe National should eventually become a secondary airport, which it should for both safety and anti-pollution reasons. It is inevitable that a rebuilding of National will occur if Mr. Goldschmidt's proposals are adopted and that it will remain the region's dominant airport for at least another generation.

Within the framework he chose, however, Mr. Goldschmidt has made the right choices. He wants to shut down National at 10:30 p.m. and cut from 60 to 18 the number of operations (takeoffs and landings) now permitted there after 9 p.m. He also wants to switch four operations an hour from the big jets of the major airlines to the smaller planes of the commuter airlines. While the latter move will not have much impact on noise levels, the former should make it possible for those who live under the flight patterns to sleep better (and longer) each night.

The most importanat of the propsals, however, is the one that would permit the new two-and three-engine wide-body airplanes to use the airport. Although they carry more passengers, these planes make less noise than those now in use. By letting them operate out of National and by limiting the number of passengers at the airport to 18 million a year, Mr. Goldschmidt hopes to reduce, eventually, the total number of flights.

The one jarring note in his proposals is the reopening of debate on the "perimeter" rule. This rule forbids flights of more than 650 miles from coming into or going out of National except for those that provide service to and from seven specific cities. The rule is a compromise between the FAA's original proposal, a decade ago, of a 500-mile limit and the demands of Midwestern politicians that nonstop flights be available from National to Chicago and St. Louis. Given the bitterness of the fight from which that compromise emerged, it would be better to keep the issue closed. But Mr. Goldschmidt has suggested expanding the perimeter to 1,000 miles -- which, just incidentally, will accommodate politicians from Louisiana and southern Florida.