Mayor Giuliani is celebrating his birthday the way many political candidates do: He’s raising money.

Mr. Giuliani will be barnstorming the city today to collect money and curry support for his presidential bid in Republican strongholds that twice helped elect him mayor.

The GOP presidential hopeful, who turned 63 yesterday, is hosting fund-raisers in four of the city’s five boroughs. The only borough he’s not hitting is Manhattan, where he’s already raked in large amounts of cash.

The point of holding fund-raisers in New York but outside Manhattan is to show that his supporters “aren’t just fat cats,” a history professor who has worked as a speechwriter for Mr. Giuliani, Fred Siegel, said.

“He’s saying, ‘I wasn’t the Manhattan candidate as mayor, I’m not the Manhattan candidate as president,'” Mr. Siegel added.

Mr. Giuliani’s day will start in the Bronx at City Island’s Sea Shore Restaurant. The general manager of the restaurant, John Mandy, said he’s expecting about 150 guests for the continental buffet breakfast.

Mr. Mandy said the last presidential candidate the restaurant hosted was a 1984 Democratic hopeful, Walter Mondale.

After the Bronx, Mr. Giuliani will head to Queens for a lunchtime fund-raiser. Then he’s off to the Bay Ridge in Brooklyn and to Staten Island, where he has always had strong support.

Rep. Vito Fossella, a Staten Island Republican, said tonight’s event would draw a standing-room-only crowd of several hundred supporters.

The Giuliani campaign would not disclose how many combined supporters it is expecting at the events or how much money it will raise.

According to the Daily News, tickets for the day’s events start at $250, but go way up from there.

State Senator Martin Golden — who is on the host committee of Mr. Giuliani’s Bay Ridge fund-raiser — said he expected about 300 people at the Brooklyn event, which take in “well over $100,000.”

“These are people who have seen Rudy through his years here as mayor of New York,” Mr. Golden said. “They have seen what he is capable of and how he took an unmanageable city and made it manageable.”

Not everyone has such glowing things to say about Mr. Giuliani. Some are expecting protesters today.

At previous fund-raisers, he has been met by protests from families of World Trade Center victims and firefighters, who are critical of how he handled the city’s emergency preparedness and its response to the attacks.

Depending on how much traction that criticism gets nationally, it could prove damaging to Mr. Giuliani, whose campaign is largely focused on his national security credentials and his leadership in the aftermath attacks.

Mr. Siegel said Mr. Giuliani’s response to any protests could be the most interesting aspect of his four-borough swing today.

“Will he handle this better than he handled abortion in the first debate?” Mr. Siegel said. “Campaigns are tests. How do you handle pressure?”

Mr. Giuliani spent much of last week picking up endorsements from Republicans in New York.