WASHINGTON — Neither Senator Clinton nor Senator Obama has released detailed plans to enact universal health care if they are elected to the presidency, but already a key difference has emerged on the issue: Mr. Obama says he can get it done four years faster.

The Illinois senator has repeatedly said universal coverage should be achieved by the end of his first term as president, while Mrs. Clinton has pledged to reach the goal by the end of her second term as president. The candidates have not explained the contrasting timetables, but Mrs. Clinton’s eight-year window underscores her multipronged approach to universal coverage on the campaign trail.

Although she promises at nearly every turn to succeed where she failed in the 1990s, she stresses equally as often that a president cannot enact a universal health plan single-handedly. Drawing on the “scars” of her experience during her husband’s administration, Mrs. Clinton has instead framed the issue as requiring a nationwide “movement” that will yield a broad consensus for universal coverage, along with a filibuster-proof Democratic Congress to see it through.

“This is going to be a big political battle,” Mrs. Clinton said Saturday in Las Vegas at a candidate forum on health care sponsored by the Service Employees International Union and the Center for American Progress. She pointed out that the bill she spearheaded during President Clinton’s first term was ultimately stymied by a Republican filibuster in the Senate. The Democrats, therefore, would need to pick up several seats in 2008 to gain the 60 votes needed to overcome the parliamentary maneuver.

A two-term time frame could allow for the political fight to take place, or it could factor in a longer transition period that might mitigate the initial cost of implementing a plan for universal coverage. As proposed in 1993, the original Clinton health care plan would have been fully implemented within four years.

“I think that is probably showing caution,” a former lieutenant governor of New York, Elizabeth McCaughey, said of Mrs. Clinton’s approach. Ms. McCaughey’s detailed critique of the Clinton health plan in 1994, published in the New Republic, was seen as a factor contributing to its demise in Congress.

An estimated 47 million Americans are now uninsured, and the issue has dominated the domestic policy debate in the Democratic primary. Mrs. Clinton, despite not having issued a complete proposal, has focused on health issues constantly. She appeared in a health forum in Iowa yesterday, televised live on ABC’s “Good Morning America.”

The difference in health care goals could also factor into Mrs. Clinton’s strategy of portraying herself as the most experienced candidate — her timeline may be seen as more realistic and feasible than those put forth by other presidential contenders, including Mr. Obama and a former North Carolina senator, John Edwards.

“Is this Hillary saying she’s campaigning for a second term already?” a health economist at the American Enterprise Institute, Joseph Antos, said of her eight-year timetable on health care.

While expressing skepticism that a plan for universal coverage in the Democratic mold could ever be achieved, Mr. Antos said two terms was a more realistic goal, given the political lift it would take. “You have to plow before you plant your seeds,” he said.

Mrs. Clinton was asked directly in Las Vegas whether the other candidates, who pledge to implement universal coverage in their first term or sooner, were being unrealistic. “Well, I think we all are going to try to start as soon as possible,” she replied, before pointing out that President Bush’s Medicare prescription drug plan, which she opposed, has taken more than three years to execute since it passed Congress in 2003. “I think we can move more quickly,” she said, “but make no mistake about it. This will be a series of steps.”

Mr. Edwards was the first of the leading Democratic candidates to release a detailed health plan, and he has been blunt in saying tax increases would be needed to pay for it. The proposal would “insure all Americans by 2012,” according to a summary on his campaign Web site. At an estimated cost of $90 billion to $120 billion a year, it would expand the current employer-based system rather than instituting a nationwide single-payer system similar to those in Canada and Britain. A government plan would be one of several options people could choose.

Despite suggestions from Mr. Edwards that universal coverage is impossible without additional revenue sources, Mrs. Clinton and Mr. Obama have neither committed to nor ruled out raising taxes. The former first lady has emphasized the need to reduce health care costs, and she has said she does not want to put more money into a “broken system.”

Mr. Obama is expected to ramp up his participation in the health debate in the coming days. He will begin holding a series of “community meetings” on health care beginning next week, his campaign said yesterday. “Right now, he’s focused on listening to real people across the country, and he’ll be rolling out his health care plan in the coming months,” a spokeswoman, Jennifer Psaki, said.