Thousands of Buddhists filled Washington yesterday for an "Aloha, we love America" festival complete with a display of 10,000 American flags, Polynesian dancing and fireworks, all but eclipsing the efforts of a women's anti-nuclear war group celebrating Peace Day on the Mall.

The Buddhists, who are members of Nichiren Shoshu Soka Gakkai of America, part of a religious organization with a large political party in Japan, staged a high-spirited parade along Constitution Avenue and then gathered on the grounds just west of the Washington Monument.

NSA bills itself as the largest Buddhist organization in America, claiming 250,000 members. Yesterday's events capped a two-day weekend celebration -- Saturday night featured a massive fireworks show and a concert with Herbie Hancock and Tina Turner -- in honor of the 25th anniversary of NSA's founding in the U.S.

The celebrants had come, mostly by bus, from all over the country. An NSA spokesman said the group bused in 24,000 of its members, and Park Police estimated yesterday's crowd at about 15,000. They created a sea of blue and white in the city yesterday as they all dressed for the occasion in white shirts and white pants or skirts and blue NSA baseball caps.

Critics and former members of the group call it a cult, and counter-demonstrations were planned, including a protest staged Saturday night by eight members of the Citizens for Freedom Foundation, an anti-cult group from Chevy Chase.

While 400 NSA members from Hawaii, who seemed ill-clad for the chilly weather in their grass skirts and leis, danced to island music on the Monument Grounds, the members of the Greater Washington area chapter of Peace Links -- Women Against Nuclear War -- presented speeches and folk music before a handful of people around the pond at Constitution Gardens.

Patricia Roberts Harris, former U.S. Cabinet secretary, made the opening remarks and introduced the speakers, who included Barbara Levin, wife of U.S. Senator Carl Levin (D-Mich.); Paul Warnke, former director of the U.S. Arms Control and Disarmament Agency, John Steinbruck, pastor of the Luther Place Church, and Mayor Marion Barry.

"What happened in Hiroshima and Nagasaki must never happen in this world again," Harris said.

The other speakers talked about the value of human life and urged an end to nuclear war. "We must celebrate peace in order to avoid war," Barbara Levin said. "This is a people's movement to influence government."

Similar Peace Day celebrations were staged yesterday in Arkansas, Iowa and Tennessee. Barry proclaimed yesterday Peace Day in the District of Columbia and urged the members of Peace Links, a group founded last year by Betty Bumpers, wife of U.S. Senator Dale Bumpers of Arkansas, not to be discouraged by the poor turnout.