The San Francisco Democrat, speaking at a news conference in the city, said health care cooperatives are "not a substitute" for a government-backed alternative.

Pelosi's comments came as the White House has been forced into damage control this week after it appeared the Obama administration might be backing away from a public plan, which would compete with private insurance companies and give consumers an alternative to that coverage.

"I agree with the president when he said a public option was the best way to keep the insurance companies honest, that it would be the best way to increase competition so that we can lower costs, improve quality of care, retain choice and expand coverage," Pelosi said.

A better idea anyone?

"If someone can come up with a better idea, let them put it on the table. But we haven't heard that yet."

Pelosi insisted that President Obama has not retreated from a public option plan and said of health care cooperatives: "If someone thinks that a co-op can work for their state, that's fine. Perhaps that could be included in their legislation. But it is not a substitute for a public option."

Co-op supporters

Supporters of the co-ops say they would be able to provide insurance to members and be controlled by those members, while still providing competition and lower prices.

Obama, speaking Thursday to a national health care forum in Washington, D.C., said a public option is "just one option," although he argued it would give consumers more choice, lower costs and better health care.

"There's been a lot of confusion about this, so let me just clarify. I think a public option is important," he said at the event. "If we have a public option, that can help keep insurers honest; it can provide a benchmark for what an affordable basic plan should look like," while providing more competition that will lower costs.

"I want everybody to be clear that the public option is just one option. It will be voluntary. Nobody is talking about you having to be in the public option," he said. "The only thing that we're talking about is this being available to you as a choice, expanding consumer choice."

Progressive groups and political leaders have stepped up the pressure for health care reform as conservatives have criticized the efforts as a costly expansion of government that could put private insurers out of business and force employers to abandon their current coverage.

S.F.'s model for reform

In San Francisco, national AFL-CIO President John Sweeney appeared with Mayor Gavin Newsom to praise Healthy San Francisco, the city's universal health care program, calling it a model for reform needed nationwide to help America's 46 million uninsured.

Pelosi, at her news conference, cautioned that efforts to scale back or split the health care bill could derail reform efforts, which she called "an opportunity - not of a lifetime but of a century."

"If we don't pass this bill, with all the comprehensive aspects of it now, I don't know when we'll have a chance to do it," she said. "Does that mean that we couldn't improve upon it with future legislation as we see how it is implemented? No. But I think we have to be careful about splitting it off."

Pelosi insisted the legislation will go forward, with or without Republican support.

"The president has said that he wants to have a bipartisan bill," she said. "But we will have a bill."

E-mail Carla Marinucci at cmarinucci@sfchronicle.com.

This article appeared on page A - 1 of the San Francisco Chronicle