WASHINGTON — The political battle over how to reduce the ranks of the uninsured is escalating here, with Senator Clinton launching an attack on President Bush’s plan for tax incentives for health insurance and her 2008 presidential rival, Senator Obama, calling for universal health care by 2012.

Welcoming Mr. Bush to the politically thorny health care debate, Mrs. Clinton said yesterday that she would send him a “suit of armor”; she then criticized his proposal to change the tax code in an effort to make coverage more affordable.

“I’m going to send him a suit of armor, because I know that anybody that puts a foot into the health care debate is going to need that,” Mrs. Clinton told the U.S. Conference of Mayors, drawing laughter for her reference to her own failed attempt to enact universal health care during her husband’s administration.

In a 27-minute address to hundreds of city leaders from across the country, Mrs. Clinton touched on a range of domestic issues in what amounted to an early presidential stump speech.

Declaring a sustained commitment to universal health care, Mrs. Clinton said Mr. Bush’s plan, which would offer tax breaks to people who buy private insurance, fell short because it would take money away from public hospitals. “That is the robbing Peter to pay Paul that I just don’t think makes sense,” she said. “We shouldn’t be setting up these false choices.”

Her remarks came as one of her chief rivals for the 2008 Democratic nomination, Mr. Obama, delivered his own bold call for an expanded government health care system, saying the country should enact a universal health plan within six years. “In the 2008 campaign, affordable, universal health care for every single American must not be a question of whether, it must be a question of how,” the first-term Illinois senator told the Families USA Conference yesterday in Washington.

Mr. Obama, who formed a presidential exploratory committee earlier this month, has pushed for universal health care before, but his speech yesterday followed a concerted effort by Mrs. Clinton to raise the issue as she began her own bid for the White House. The two candidates have said they each plan to lay out more detailed proposals during the campaign. Mrs. Clinton’s speech at the Capital Hilton hotel offered a heavy dose of nostalgia for the Clinton years. The former first lady, considered an early frontrunner for the Democratic nomination in 2008, pledged to restore federal funding for police officers to its levels in the last decade. And in decrying the Bush administration’s response to Hurricane Katrina, Mrs. Clinton said the Federal Emergency Management Agency “worked in the 1990s but has failed in the last six years.”

The mayors greeted Mrs. Clinton warmly, giving her a standing ovation before and after she spoke. Mayor Bloomberg did not attend; he was in New York delivering his preliminary city budget. Earlier, Mrs. Clinton met privately with a group of mayors from South Carolina and Iowa, which is the early caucus state she will visit on Saturday for her first trip since announcing her candidacy last weekend.

For the senator, the meeting provided a chance to show off her personal touch and, apparently, her campaign’s research skills. The Republican mayor of Myrtle Beach, S.C., John Rhodes, said Mrs. Clinton turned to him while they stood for a photo and asked, “Do you really have a gold Jaguar convertible?”

Mrs. Clinton had evidently seen a profile of Mr. Rhodes earlier this month in his local daily newspaper, the Myrtle Beach Sun News, which mentioned the luxury car. Mr. Rhodes came away impressed. “Obviously, she’s a very, very brilliant person,” he said.

The Iowa trip this weekend will give Mrs. Clinton several more intimate settings to make similar connections with Democratic activists in the state that holds the nation’s first caucus a year from now. She is scheduled to attend a Democratic committee meeting in Des Moines on Saturday and will conduct what her campaign is calling a “town hall-style conversation” with Iowans there later in the day. She also will attend house parties in Cedar Rapids on Saturday and in Davenport on Sunday. In advance of the trip, the Clinton campaign yesterday announced the hiring of a veteran Iowa political operative, JoDee Winterhof, who will run Mrs. Clinton’s statewide efforts.

Mrs. Clinton and Mr. Obama also each met separately in Washington yesterday with the Reverend Al Sharpton, who has not ruled out a presidential bid himself. Rev. Sharpton, who ran unsuccessfully in 2004, also met with Senators Dodd and Biden, who are seeking the Democratic nomination.

Rev. Sharpton told reporters that the meetings went well but that he would make no decision on an endorsement or his own candidacy until late spring.