An estimated 50,000 spectators turned out for Washington's 12th annual St. Patrick's Day parade yesterday, a gala that celebrated Irish heritage and highlighted the political divisions within Ireland, but primarily delighted young and old with music, pageantry and green.

"Every nationality needs something like this," said Kevin McGrath, 28, a Metro employe from Berwyn Heights who sat with his 14-month-old son Kevin at curbside of the mile-long Constitution Avenue parade route, which was dotted with green carnations, balloons, shamrocks and more green.

"Everybody came here from someplace else and you need a day to remember that and celebrate it . . . . That's what America's all about," McGrath added. "Besides that, it's a good-time holiday" that signals the coming of spring.

McGrath's son Kevin, wearing a green-trimmed bib that said, "I'm a Happy Irish Baby," sat wide-eyed in his stroller watching the phantasmagorical procession of high-stepping marching bands, drill teams, fire engines, dancing girls, bagpipers, Irish wolfhounds, cartoon characters, unicyclists, politicians and aging leprechauns wearing green suits.

This year's most exotic group was the 65-member St. Patrick's High School marching band of Singapore. The troupe of Asian youngsters provided a mix of cultures as its two 10-foot multicolored Oriental paper dragons danced to the music of an Irish jig.

From its origins in 1971, when several hundred Irish diehards marched around Dupont Circle, Washington's St. Patrick's Day has grown into a big-league event, drawing more than 150 bands, floats and displays, said Matthew J. Hannon, a Rockville food broker who is the parade committee chairman.

"We try to keep it nonpolitical," said Hannon, who added that the annual parade only began growing in size in recent years after the local Irish-American community decided to bury its differences over the British role in Northern Ireland and unite to celebrate the holiday.

Yesterday, however, those differences were still evident as opponents of British presence in Northern Ireland distributed leaflets along the parade route and marched in the parade behind several banners, including a large black memorial to Bobby Sands, the prisoner who died last year in a highly publicized hunger strike.

When the anti-British marchers from Irish Northern Aid passed the parade reviewing stand at the Ellipse, Tadhg O'Sullivan, the Irish ambassador to the United States, left his seat and walked off the stand.

O'Sullivan, who earlier had welcomed the crowd by declaring it "a great day for the Irish and a day for the Irish to be proud," said in an interview that he left the stand because his government opposes groups that support the Provisional Irish Republican Army.

Jean Wagner of Washington, a spokesman for Northen Irish Aid, whose green button said "Brits Out, Peace In" said she resents the Irish government's portrayal of her group as supporting terrorism. She said the group marched yesterday "to remind people that the Irish people are not terrorists. They just want freedom."

Washington's mayor, who introduced himself as "Marion O'Barry," led the procession by riding perched on a plaid blanket on the front hood of a black automobile. The mayor waved a green hat. "It was easier than walking," he explained. He and other politicians drew polite applause from a crowd that appeared more interested in attractions such as a tiny marching Dachshund wearing a green scarf.

Like politicians, various entrepreneurs also seized the opportunity for some free advertising. Several had rented limousines or arranged floats that advertised Irish pubs, delicatessens, and other businesses.

A troupe of marchers carried signs calling on Washington developer Oliver T. Carr not to tear down the Rhodes Tavern.

Mostly, the parade was for youngsters such as Ann Casey Campagnolo, 9, of Silver Spring, who was so excited that she nearly jumped out of her shiny patent-leather shoes as she waited for the parade to start. "I like the parade 'cause I love to dance," she explained.

At midafternoon, she finally got her chance to do a proud jig down the center of Constitution Avenue, past the applauding onlookers.