New Yorkers and visitors from all over the globe lined Manhattan's Fifth Avenue a dozen deep for the world's oldest and largest St. Patrick's Day parade Wednesday, as crowds gathered along sun-warmed routes in Dublin and cities around the U.S. to mark the holiday.

The day simultaneously served as a celebration of spring in many cities, with participants in parades and other outdoor gatherings basking in temperatures in the 60s after a harsh winter.

The 249th St. Patrick's Day extravaganza in New York City was to be the last of the Big Apple's world-famous parades to take place before new restrictions go into effect April 1 requiring all parades to be shorter to save money.

The city issued the new rules in February, requiring all parades to trim routes by 25 percent and reduce time to less than five hours, changes estimated to save $3.1 million in police expenses.

On Wednesday, Glen Gagnier of the 198th Army band lugged a 25-pound tuba up the 2.1-mile route from 44th Street to 86th Street but said it was so exhilarating he would have marched double the distance.

"When it's done I'll want to do it all over again," he said.

Some welcomed the idea of a pared-down event.

"It'll be good because people will be able to get where they're going easier," said Yogesh Pai, of Henderson, Texas, as he navigated the crowd with his 5-year-old son.

St. Patrick's celebrations around the country and in Dublin featured threads of the same — bagpipes, marching bands and crowds eager to see spring weather.

There was a mix of lighthearted cheer and serious politics at the White House, where President Barack Obama met with Irish Prime Minister Brian Cowen.

Obama noted that 36 million Americans claim Irish ancestry, adding, "I'm sure more do on St. Patrick's Day."

"And it's a testament I think to how close our two countries are that America has been shaped culturally, politically, economically by the incredible contributions of Irish Americans," he said.

As part of a marketing deal by Ireland's tourism agency, major world landmarks — including the Sydney Opera House, the London Eye, Toronto's CN Tower and New York's Empire State Building — were bathed in green lights.

The day is named after St. Patrick, who introduced Christianity to Ireland about 1,500 years ago and became the country's patron saint.

More than half a million people lined the 2-mile route of the flagship Dublin parade, which had a theme this year celebrating the global spread of the Irish.

Mixed in with the usual displays of U.S. marching bands and Irish sporting heroes were dancing troupes from Africa and India, bands from Austria and France, giant insect floats from Spain, and Dubliners dancing with mops and dusters.

In Savannah, Ga., organizers put up crowd control barricades for the first time in preparation for large numbers at the city's 186th St. Patrick's Day parade, and Columbus, Ohio, had a record 121 marching groups including Irish clubs, police and fire departments and pipe and drum bands.

For some, the day was steeped in tradition. For others, like 9-month-old New Yorker Pasquale Ferrarelli, it was the only fitting occasion to wear a T-shirt reading "My 1st St. Patrick's Day" and a matching bright green top hat.

His mother said the Fifth Avenue parade was the first stop before the family would gather later at home on Long Island for corned beef and cabbage, and soda bread.

"And we'll eat, drink, dance and sing," said Jennifer McLaughlin-Ferrarelli.

Politicians seized the moment, too, to appear before large crowds and soak up attention in what is shaping up to be a busy election year. Republican gubernatorial candidate Rick Lazio marched the route, and so did his potential primary opponent, Suffolk County Executive Steve Levy.

Representatives of lesbian, gay, bisexual and transgender groups were not allowed to participate in the march — at least, not under their own banner. Members of the Ancient Order of Hibernians, who run the parade, argue they may invite whomever they please.

Outgoing Gov. David Paterson, who is being investigated over free Yankees tickets and whether he made illegal contact with a woman who made a domestic violence complaint against a top aide, skipped the parade after attending morning Mass at St. Patrick's Cathedral with Mayor Michael Bloomberg.

Bloomberg — not currently running for anything — marched while waving an Irish flag.

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Associated Press writer Shawn Pogatchnik in Dublin contributed to this report.