The announcement came after Mr. Bloomberg gave a speech denouncing partisan gridlock in Washington, stirring renewed speculation that he is preparing to run for president in 2008 as an independent or third-party candidate.

“I have filed papers with the New York City Board of Elections to change my status as a voter and register as unaffiliated with any political party,” he said in a statement issued while he was in California delivering political speeches.

“Although my plans for the future haven’t changed, I believe this brings my affiliation into alignment with how I have led and will continue to lead our city,” the mayor said.

Records show the mayor — who happens to be swinging through San Francisco and Los Angeles starting today — has visited 20 U.S. cities in the last 18 months.

And that doesn’t count Albany or Washington, routine stops on the government circuit, or foreign countries such as Israel, Jordan, Ireland and Mexico that Bloomberg visited this year alone.

By comparison, in 2004, he took a total of 10 out-of-town trips. Five were to overseas destinations and three were to Albany and Washington.

In 2005, an election year, Bloomberg scaled down. Not a single U.S. city, outside of Albany, made it onto his itinerary.

Over the last 12 months, however, Bloomberg has hit enough cities on his private jet to qualify as a travel-guide writer.

His comments suggested that two hours of testimony by Mayor Bloomberg at an Assembly hearing on Friday had not swayed the Democrats who control the chamber. Mr. Silver even seemed to outline new concerns, saying that the plan could actually hurt areas with high asthma rates.

“The children of the South Bronx, Bedford-Stuyvesant and Harlem, among others, are the ones who have been exposed to a lot of pollutants,” he said. Not only would those neighborhoods not benefit from the plan, he said, “some of those areas will become parking lots with people driving around the neighborhoods looking for parking spots in order to avoid congestion pricing fees.”

“There is a plan that can be put together that would obviously alleviate the environmental negativism of what takes place in Manhattan right now,” he said, but added that it could be done “with or without” congestion pricing.

. . .

But Mr. Silver’s remarks underscored that he may once again serve as the mayor’s foil in Albany. His opposition doomed the mayor’s plan to build a West Side football stadium for the New York Jets. Asked about parallels to that battle, Mr. Silver harked back to the mayor’s contention then that a Manhattan stadium would not cause undue congestion.

The stadium, Mr. Silver pointed out, would have been “right in the middle of this congested zone.”

“At that time, a year ago, there obviously was no congestion,” he added, facetiously. “We can even put this stadium to attract 100,000 people to come in right in the middle of the zone and there was no problem.”

. . .

Mr. Silver’s skepticism partly reflects the wide concern about the plan among the more than 100 Democrats who control the Assembly.

“I’m sort of torn here,” said Assemblyman Ruben Diaz Jr., a Bronx Democrat. “On the one hand, I really want to address the environmental issues,” he said, but added that he was concerned that congestion pricing could mean “that folks from other places are going to park their cars in my community” or that the toll would end up being a tax on his constituents without much benefit.

“I think in its present state,” he said, “there are too many concerns, certainly for us to rush to any judgment.”

After marching in the Laurelton Memorial Day Parade, Bloomberg made a push for his plan, calling it a “win, win, win, for everybody.”

“Our soldiers are fighting so that we have our freedoms. Unless you have good health, you’re not going to be around to enjoy them,” Bloomberg said.

“The pollution that’s going into the air today is causing our kids in a lot of neighborhoods in New York City to have four times the national asthma rate.”

The mayor enlisted a group of environmental activists to buttress his case and emphasized that the city’s air is simply not good enough.

“It is not healthy for you; it’s not healthy for our children yet to be born, or our children who are here today.