After five days of impeccable early fall weather, Washingtonians were hoping yesterday that summer, which has been known to perform some highly unwelcome encores in past years, may have exited on schedule this year for once.

The National Weather Service offered qualified encouragement, predicting "more of the same" for today and tomorrow, and a cool weekend with a chance of showers Sunday.

"But we do many years get periods of warmer and more humid weather into October," cautioned forecaster Charles Chilton. It's too early to say whether such unpleasant will recur this year, he added.

Those considering trips to the Blue Ridge or other forested zones can expect vivid autumn colors, according to William Stanley, a land system analyst for the University of the District of Columbia's D.C. extension service.

Greater than average rainfall in August and clear weather so far in September should produce a quicker and more striking shift to the reds, oranges, yellows and browns of autumn, Stanley said, adding a "guesstimate" that trees in the Washington area will begin turning color in about two weeks and produce their most dramatic display in about a month.

Yesterday was the fourth day of the last five on which afternoon temperatures remained in the 70s. For Bob MacDonald and Albert Formando, two Metrobus driver who got off work at 1:30 p.m., it was "ideal weather" to play nine holes of golf in East Potomac Park.

Tourists were equally appreciative. The Faig family of Sacramento, Calif., took a quiet lunch at one of the picnic tables outside the Library of Congress, between stops on their walking tour of the Capitol and the Mall. "We've sure enjoying it," said Milton Faig. "We've had good weather all the way."

Congressional employes took advantage of the postcard weather to eat, read and lounge on the lush grass of Capitol grounds. Under a dazzling blue sky and with the Capitol as a backdrop, two members of Congress talked about the natural gas compromise to television interviewers, and a candidate filmed a commercial for his campaign.