WASHINGTON — Kicking off what is sure to be a frenzied four-month sprint to the Democratic presidential primaries, Senator Obama of Illinois and John Edwards are taking aim at Senator Clinton’s embrace of a Washington political system that they say was broken even during her husband’s time in the White House.

A day after Mrs. Clinton touted her experience in Washington and said she would “work within the system” to effect change as president, Mr. Obama shot back that the “system isn’t working for us and hasn’t for a long time.”

Mr. Edwards, a former North Carolina senator, countered that Mrs. Clinton “defends Washington lobbyists” and referred derisively to her failure to enact universal health care as first lady.

The rhetorical jabs come as Messrs. Obama and Edwards seek to establish themselves as Washington “outsiders” and cast Mrs. Clinton as wedded to the special interest culture, in an effort to erase her lead in the polls.

All three leading Democrats were barnstorming the early primary states on Labor Day, courting union members and reaching out to voters who may only now be paying attention to a campaign that began eight months ago.

Mrs. Clinton enters the fall as the clear front-runner, maintaining a double-digit lead in national polls and most early primary state surveys. The one exception is Iowa, the state that traditionally holds the first caucus and where Mr. Edwards is pinning his hopes on a victory that will give him momentum in subsequent primaries. He is running neck-and-neck with Mrs. Clinton and Mr. Obama in the polls there, although he trails them both nationally.

On Sunday, Mrs. Clinton unveiled an updated version of her stump speech in which she said her long years in the nation’s capital — a source of increasing criticism from her top Democratic rivals — would serve as an advantage in achieving reforms in health care, the environment, and other priority issues.

“From my time in the White House and in the Senate, I learned you bring change by working in the system established by the Constitution,” she said in New Hampshire. “You can’t pretend that the system doesn’t exist.”

Mrs. Clinton repeated the theme while campaigning with President Clinton in Iowa yesterday, saying, “We need to focus on results, not rhetoric, people not process,” the Associated Press reported. She returns today to Washington, where she will address the Alliance for Retired Americans.

Mr. Obama rolled out a retooled stump speech of his own yesterday, and while a campaign spokeswoman said it had been in the works for weeks, it included an unmistakable rebuttal to Mrs. Clinton.

“There are those who tout their experience working the system in Washington — but the problem is that the system in Washington isn’t working for us and hasn’t for a long time,” Mr. Obama said at a rally in Manchester, N.H., according to a text provided by his campaign. Referring to health care and other issues, he added that “through Democratic and Republican administrations, we’ve failed to act.”
Taking a veiled swipe at the Clinton legacy, he also said: “George Bush and Dick Cheney may have turned divisive, special-interest politics into an art form, but they didn’t invent it. It was there before they got to Washington, and if you and I don’t stand up and challenge it, it will be there long after they leave.”

Messrs. Obama and Edwards have been sounding similar themes in recent weeks, with the 2004 vice presidential nominee adopting a more confrontational tone. Mr. Edwards yesterday highlighted his differences with Mrs. Clinton over the political environment in Washington in an appearance on ABC’s “Good Morning America.”

“She and I have a big disagreement on this,” he said. With a reference to Mrs. Clinton’s unsuccessful bid to overhaul the health care system in the 1990s, he added: “Senator Clinton defends Washington lobbyists and the system that exists in Washington. She thinks she can work within that system. If that were true, we would already have universal health care.”

Mr. Edwards’s campaign received a boost yesterday with the Labor Day endorsements of the United Steelworkers and the United Mine Workers of America. Mr. Edwards has been courting unions aggressively, and after the endorsement of the United Brotherhood of Carpenters and Joiners last week, he boasted of having more union support than any of his rivals.

Several major labor groups have yet to pick candidates, however, and their decisions could be key to Mr. Edwards’s chances in the early primary states.

In a statement announcing the endorsement, the president of the steelworkers union, Leo Gerard, said Mr. Edwards was “the candidate with the best chance of winning in the general election,” echoing a message the Edwards campaign has been trying to focus on lately.