Sunshine, exotic foods, big-name jazz greats, Caribbean music, and the antinuclear movement drew thousands of people outside yesterday as Washington got a preview of the sights, sounds and smells of summer on Memorial Day weekend.

The Tidal Basin was awash with bright blue paddle-boats, while the nearby Mall filled with tourists and noisy games of lacrosse, volleyball, baseball and frisbee. Tourmobiles and souvenir vendors were in high gear, and near the Ellipse, Ronald Wells, a 21-year-old George Washington University student, had sold enough ice cream sandwiches by midday to convince him that "summer is coming."

The temperature climbed to 85 by mid-afternoon, with 65 percent humidity making it feel even hotter. Sunshine gave way to severe thunderstorms by early evening. The National Weather Service forecast a 20 percent chance of rain today, with temperatures up to 90 degrees..

"Feels like summer is here now, man," said Stetson King, a Trinidadian drummer, sweating heavily as he rolled six steel oil drums into place, getting ready to entertain a sun-drenched crowd of about 2,000 persons who lined the C & O Canal in Georgetown. They were there for a free concert, featuring Caribbean music and international foods.

Just a few hundred yards away, several thousand more music lovers escaped the heat at the Kool Jazz Festival at the Kennedy Center, where jazz afficionados paid up to $55 each to hear Miles Davis, Dizzy Gillespie, Benny Goodman and dozens more at daytime and evening jam sessions.

For many, it was a day of fun, food and music. But one of the largest gatherings was more serious: a two-mile "Peace Procession" and rally at Lafayette Park by a group of some 3,000 Roman Catholic nuns and other women religious protesting the spread of nuclear arms.

Organizers of the march, the Leadership Conference of Women Religious, said they believed it was the largest political gathering ever of American nuns. Coming from around the country, they gathered on a football field at Gonzaga High School on North Capitol Street for a service of prayers, songs and speeches, including that of Miyoko Matsubara, a survivor of the bombing of Hiroshima, who urged, in halting, high-pitched tones, "Let us join, in one big voice, to say: No more Hiroshima, no more Nagasaki, anywhere in the world."

Behind banners with such slogans as "Pentecost not Holocaust," the nuns marched and chanted prayers. Some burned incense and carried baskets of bread and flowers for a prayer service at Lafayette Park. Several thousand postcards were delivered to the White House, calling on President Reagan to support a nuclear arms freeze.

At the C & O Canal, the Caribbean rhythms of The Original Trinidad and Tobago Steel Band of Washington, D.C. could be heard above the waterfall at the Foundry Mall. In a tiny park, spectators were packed sardine-like in search of good sunbathing positions. Others elbowed for spots in the shade, or dangled their feet in the brackish water of the canal while they listened to music and sampled German, Lebanese, Indian, Armenian, and Chilean food, among others.

"We came for the music, but I think all these people are the most entertaining," said Judith Ogden, a mother of five from Dale City who was debating whether to sample an Armenian Luleh Kabob.

At yet another kind of gathering, some 12,000 people attended a re-creation of the Battle of First Manassas, staged by about 500 volunteers at Bull Run Regional Park in Fairfax County.

History also was explored at the Washington Marina, where 3-year-old Aaron Mathis of Arlington was among hundreds who climbed aboard the visiting clipper ship, "Pride of Baltimore." The majestic 137-foot vessel was built by the city of Baltimore five years ago to replicate the clippers of the early 1800s. After he scrambled around the ship's rigging and admired its 95-foot Douglas fir masts, Aaron declared: "I wike it."