Summer already seems a memory. The pickup softball games have, for the most part, ended. Touch football starts this weekend. The white and pastel-colored dresses and sandals, and the bare legs that looked so perfect just a few weeks ago seem foolish now, like something from a scrapbook of summer past. Along the path in Rock Creek Park there is the thinnest carpet of fallen leaves. Even the office bulletin boards have changed: Gone are the ads for beach cottages in places like Rehoboth, Ocean City, Nantucket and Martha's Vineyard. The weekends of summer are over. They were not, after all, endless.

Washington, after a few carefree months, seemed yesterday to have returned to its normal, workaday rhythms, its only solace a brilliant fall day.

The president is back at the White House, and though assistant press secretary Mark Weinberg claims the pace around there never slowed, he will concede one seasonal change: The correspondence unit is already putting together the White House Christmas card list. Congress is back in session. The college students are back, too, and the Georgetown University bookstore has already had to reorder such classics as "The Communist Manifesto," "Mastering Organic Chemistry," "Madame Bovary," "Great Expectations," "Heart of Darkness," and "The Basis for Accounting Decisions."

Bookstore clerk Mark Montefiori, 24, pronounced himself "rather indifferent" to the start of the new academic year and said he was more interested in dreaming up ways to get rich. His own fall reading list includes "Leadership Effectiveness Training," "Capital and Job Formation" and "The Sorrows of Young Goethe."

John Barreto, 25-year-old manager of Britches Great Outdoors on Wisconsin Avenue, was in high spirits yesterday, exulting over the cool weather that turned the thoughts of young preppies everywhere to corduroy pants in colors like plum, taupe, lavender, pewter, royal blue, slate blue and sea foam green.

"The colors are just fabulous!" he said, clad, on this autumn-like day, in navy blue corduroy pants, one of 20 pairs he owns. By noon, he had sold 30 pairs of corduroy pants. He still talked of the New Jersey contractor who three weeks ago bought enough fall clothes to fill five big bags.

"He said he didn't need heavier shoes because he has a Rolls-Royce and if his feet get cold it means something's wrong with the car."

In parks and in window boxes, the marigolds and begonias and impatiens and geraniums still bloom. The scarlet sage is brilliant. But the petunias and the asters are fading, even as the first leaves on the red swamp maple trees turn red. Soon, the National Park Service will plant 17,000 white, rust, red and yellow chrysanthemums around the city.

The streets of Washington yesterday were a sea of sweaters and blazers, and it was possible for the first time in what seemed like many weeks, to walk more than a few blocks without encountering someone holding one of those ubiquitous green, white and yellow paper cups marked Yummy Yogurt. Men kept their jackets on when they went to lunch. Women wore stockings. The weather was kind to the bag ladies, who looked so out of place all summer in their heavy coats and woolen hats. At this time of year, they begin to look less strange.

The low temperature was 59 degrees. The high was 80. There were electric heaters on the shelves at some of the Safeway stores, and at the Drug Fair at 15th and L streets NW, there remained only one bottle of Sea & Ski Dark Tanning Oil and one bottle of Sun In.

The cover of last week's New Yorker Magazine, still on the newsstands yesterday because of the Labor Day holiday, captured the sadness of the day: It was a drawing of a man in bermuda shorts and a short-sleeved shirt, standing on a rock before the ocean, lifting his straw hat in farewell.