The most controversial proposal in the emerging debate is to create a so-called public option, beyond Medicaid and Medicare, as an alternative to private insurance. Obama supports that. He has said that would keep private insurers honest and efficient because they'd have to compete.

Insurers and other skeptics contend that a public option ultimately would run private insurance out of business and force all Americans into government coverage.

Offering universal coverage could cost between $1 trillion and $1.6 trillion in the first decade alone, according to Congressional Budget Office estimates.

Obama has proposed $622 billion in health-care cost savings, but needs more than $300 billion more to come from what Sebelius called "revenue enhancers." That could include taxing a portion of employer-sponsored health benefits. Some senators said that Obama told them earlier this month that option is still on the table.

Key senators said the idea is slowly gaining support. Sens. Kent Conrad, D-N.D., and Max Baucus, D-Mont., top Senate Finance Committee members, said Wednesday that they were looking seriously at such a tax; among the options are imposing it only on benefits above a certain cost level.

On Capitol Hill, Health and Human Services Secretary Kathleen Sebelius told the House Energy and Commerce Committee that revamping the health-care system to contain costs and cover roughly 50 million uninsured Americans is "our most important domestic priority."

Sebelius didn't rule out taxing health insurance benefits as a way to pay for such an expansion. Obama blasted that idea during last year's presidential campaign but it seems to be gaining currency as Democrats look to avoid increasing the federal deficit with an expensive health-care overhaul.

Sebelius and White House Chief of Staff Rahm Emanuel also met Tuesday night with key Democratic lawmakers.

Randel Johnson, a U.S. Chamber of Commerce senior vice president, told the House Ways and Means Committee that "requiring employers to either provide some level of health insurance or surrender a huge percentage of payroll to the government will result in job losses and lower wages.

"Whether or not this proposal is a Trojan horse for single-payer health care," he said, "it is apparent that its cause is ideological, not pragmatic."

A CBS/New York Times poll earlier this month found that 72 percent of Americans favor offering people coverage through a government plan similar to Medicare. In the same poll, 57 percent said they'd be willing to pay higher taxes in order to cover everyone.

However, an ABC News/Washington Post poll this month found 58 percent of U.S. adults were "very" concerned and another 23 percent "somewhat" concerned that the current effort would reduce the quality of care they receive. Americans also worry that changing the system could end up increasing costs, limiting choices of doctors and treatments and sharply increasing the federal deficit.