WASHINGTON — The search for agreement on health care may be short lived.

The flash point is a proposal that would give Americans the option of buying medical coverage through a government plan. President Barack Obama and many Democrats have endorsed it, as one part of a broader health overhaul. On Saturday, Republicans laid down a challenge.

“I’m concerned that if the government steps in, it will eventually push out the private health care plans millions of Americans enjoy today,” Rep. Roy Blunt, R-Mo., said in the Republican weekly radio address.

Blunt, who will play a leading role in the debate, warned: “This could cause your employer to simply stop offering coverage, hoping the government will pick up the slack.”

The proposal he referred to would, for the first time, offer government-sponsored coverage to middle-class families, as an alternative to private health plans. It could also be a deal breaker for broad, bipartisan agreement on health care.

Insurers fear competition from a government plan could drive them out of business, and Republicans worry it would lead to a government takeover of health care. Liberals, meanwhile, are equally adamant that Americans deserve the choice of government-sponsored health care.

“The purpose of health care reform is to make sure all Americans have health care, not to promote the insurance industry,” said Rep. Jan Schakowsky, D-Ill., who serves on a House panel that will help write the legislation.

Asked at the White House health care summit last week about the worries brewing, Obama promised to address the qualms felt by some. But he did not abandon the notion of a government plan, and Democrats say they will fight to ensure a public plan stays in the final bill.

A changed climate?

Sixteen years ago, the opposition that killed President Bill Clinton’s massive plan for universal health care coverage was distilled in a 30-second ad showing “Harry and Louise,” a fictional middle-class couple, shuffling papers and complaining about “government bureaucrats” who limited their choices.

But at the conclusion of the summit on health care reform, the head of the trade association of insurance companies — the successor to the group that spent millions on those commercials — pledged to support Obama’s push for a comprehensive overhaul of the health care system to cut costs and expand access.

“We understand we have to earn a seat at the table,” said Karen Ignagni, president of America’s Health Insurance Plans, addressing Obama in the gilded East Room.

In 1993-94, a plan was drafted, largely in secret White House meetings, by a task force headed by first lady Hillary Clinton. With little public input, the group coughed up a 1,324-page bill that interest groups picked apart for months. And because members of Congress had not been consulted, they either opposed the bill or, at best, were unwilling to defend something they had no hand in creating.

The Clinton plan was complex and was presented all at once, in mind-numbing detail. In contrast, Obama has been vague, preferring to build consensus around general principles. He has made clear that Congress would write the legislation; congressional leaders say they want to pass a bill this summer.

Still, hard questions lurk beneath the cheery surface of consensus. Should the government mandate that people buy insurance, or that employers provide it? How will it be paid for? Should a government health insurance plan compete with private insurers? Such an approach might get insurance to more people, but would it be unfair to private-sector firms because the government could undercut them on price?

Still, the turnabout by insurers was a striking illustration of how much health care politics have changed, analysts say. Former adversaries are agreeing that something must be done: Costs are spinning out of control, harming business and government alike, and 47 million Americans lack insurance.

“You have,” Ignagni said, “our commitment to play, to contribute and to help pass health care reform this year.”