Mayor Bloomberg will be operating in a whole new political environment, to judge by appearances the day after he rocked the presidential race with news of his defection from the Republican Party.

Dozens of news reporters and television cameras packed into the city’s 311 call center for what on any other day would have been a tame affair. Mr. Bloomberg seemed to relish the spotlight, entertaining questions about what his presidential platform would be, even while insisting that he isn’t going to be a 2008 contender.

Feeding into the already fever-pitch speculation about whether he’s going to become the third New York candidate to enter the presidential race, Mr. Bloomberg refused to pledge that he would serve out the remainder of his term at City Hall.

Instead, he left himself wiggle room, saying: “My intention is to be mayor for the next 925 days and probably about 10 hours.”

The mayor, who made several sarcastic cracks on the idea that the packed house of reporters must be covering the 50 millionth call that 311 fielded yesterday morning, indulged the questions about how he would go about fixing the federal government.

He railed against the country’s immigration policy, said federal agencies weren’t run well, talked about foreign policy, and said voters should know more about what the presidential candidates stand for.

“When they say they’re in favor of motherhood and apple pie, how are they going to make motherhood and apple pie available to everybody and how are they going to pay for it?” he said, recycling one of his favorite lines.

He vaguely touched on Iraq and Iran, topics he usually avoids, saying that a nuclear Iran would be a major cause for worry. And, in an apparent reference to resources being stretched thin in Iraq, he said: “The last thing you want to be is a superpower with your hands tied.” Tonight, he is scheduled to speak in front of the Foreign Policy Association, an event that will give him a chance to expand on his international views.

When pressed on whether there were any circumstances under which he would run, he said smirked and said: “If everyone in the world was dead and I was the only one alive? Yeah, sure. I mean, come on.”

Despite what Mr. Bloomberg is saying, his new voter registration adds to the growing mountain of evidence that he is getting serious about a run.

The backdrop for yesterday’s event, the 311 call center, seemed designed to highlight his managerial competence, which would most definitely be the centerpiece of his platform if he ran.

“You can report a pothole in Korean, ask for a nicotine patch in Portuguese, and ask about alternate-side-of-the-street in Zulu,” he said.

While Mr. Bloomberg would have significant challenges to overcome if he did actually decide to run, the threat he poses to the leading Democrat, Senator Clinton, the leading Republican, Mayor Giuliani, and the other candidates is no joke. The leading theory is that a Bloomberg bid would be far more harmful to the Democratic nominee than to the Republican.

Mrs. Clinton and Mr. Giuliani both offered measured responses yesterday to Mr. Bloomberg’s party change announcement.

After a Senate hearing in Washington, Mrs. Clinton said: “Well, I am not surprised by anyone leaving the Republican Party these days, and I’ll just leave it at that.”

Mr. Giuliani, who was on a swing through the first caucus state of Iowa yesterday, also kept his comments to a minimum.

“I like Mike very much,” Mr. Giuliani said, according to the Associated Press. “I am disappointed that he left the Republican Party. I still respect what he’s done as mayor.”

When pressed on what a Bloomberg candidacy would mean he said: “He says he’s not running, so I’ve got to take him at his word. If he does run, he has every right to do it.”

Mr. Bloomberg ran into a friend of Mr. Giuliani’s, Howard Koeppel, last night at the Sheraton in Midtown, the Associated Press reported. Mr. Koeppel was there for a Giuliani fund-raiser, while Mr. Bloomberg was there to give a speech.

“I said, ‘If you run, I would like that,'” Mr. Koeppel told reporters. “‘You’d take votes away from Hillary. You’d help the Republicans, and you’d be good for Rudy.'”

Mr. Koeppel said the mayor replied: “Don’t worry about it, I’m not running.”

Mr. Bloomberg, a billionaire who became a Republican in 2001 after years as a Democrat, has long been considered a so-called RINO, or Republican in Name Only.

To highlight just how much distance he’s had from the Republican Party to date, the White House press secretary, Tony Snow, said he didn’t know the mayor had switched parties. The news was on the cover of dozens of newspapers. “Has he made it official?” Mr. Snow said.

Mr. Bloomberg said he was just flattered by all of the coverage. “They must think I’m doing a decent job,” he said as photographers feverishly snapped pictures of him at the podium.