It was the first day of fall and it seemed yesterday as if the season itself were trying on moods. Area residents pulled on sweaters and just as quickly took them off again throughout the day; in quick and crazy succession, there were lowering clouds, fair and sunny skies, crisp breezes and frosty drizzle.

Temperatures dived from the record highs of the beginning of the week to record lows, with 33 degrees at Dulles International Airport early yesterday. For some, the cold weather alone was guarantee enough that fall was finally here.

"It's autumn," said John Boyer, eating his lunch on a ledge overlooking the C&O Canal with four other architectural graduates. "You know it's autumn when you don't wake up in a pool of sweat." But farther down the canal path, a napping sunbather lying barechested on a bench had apparently decided it was still summer.

No matter how reluctantly, it was time to notice that the days were growing shorter. Along Rock Creek Parkway copper tints became visible amid the frothy green. Caught unprepared by the chill, Georgetown resident Mary Hastings went through her summer clothes and came up with her single unpacked sweater, which she wore yesterday over a shirt. "I haven't really prepared for fall," she said. "It might be 90 degrees tomorrow."

Some homeowners were equally unprepared. In Fairfax County, two furnaces kicked on yesterday when temperatures dropped and ignited basement fires that caused an estimated $65,000 worth of damage in two suburban homes.

However unexpected, the cool weather came as a relief for many. "I'm glad fall's here," said Lauren Rosenfield, a finance student at George Washington University, browsing among the tweeds at Garfinckel's. "It's fun to go away in the summer and come back when everything is so active and vibrant."

For many, the beginning of autumn is a festive time, said Ann Stone, a clinical psychologist who is acting director of George Washington University's Health Plan. "It's the psychological beginning of the year. It comes from many years of beginning school at this time. In addition, the change of weather, the relief from the heat, is invigorating to many. It's a time to start projects."

But for others the beginning of fall marks the beginning of anxiety with almost thermostatic precision, according to Mitch Snyder of the Community for Creative Non-Violence. The community operates soup kitchens, an infirmary and shelters for the homeless at different locations throughout the city. "The moment temperatures dropped we could sense people getting depressed and angry because they know winter is coming," Snyder said.

The best that street people can hope for is that the fall and winter will be lenient. Donald Gilman, head of forecasting at the National Weather Service, said that the abnormal wind patterns that produced the hot extremes of summer are apparently over. "We should have a normal fall," he said, "with seasonal fluctuations in the weather."

In any event, even for street people, the turn of the seasons brings its own ironic relief. "Once winter comes, sheer survival occupies everybody's time and energy, but now is the time they worry," Snyder said.