WASHINGTON -- A group of conservative Republican senators put forth a plan Thursday that seeks to ensure every American has health insurance -- a cause long championed by the political left.

The bill encourages families to find their own health coverage and offers refundable tax credits of up to $5,400 per family. But advocates for the uninsured say the proposal could jeopardize low-income families and chronically ill patients, as well as the employment-based health care system, which now covers 65 percent of Americans.

"It's time for a major debate on health care insurance," Sen. Mel Martinez, R-Fla., said in a statement. "Not enough people have access to affordable health care, and the Congress has not done enough about this crisis." Martinez was joined in introducing the bill by fellow Republican Sens. Richard Burr, of North Carolina, Tom Coburn, of Oklahoma, and Bob Corker, of Tennessee.

The bill could bring health coverage to millions of Americans now without it. But Burr said in an interview that it also would begin taxing the value of health care plans that many employers now offer workers, a controversial provision sure to face opposition. Such benefits are now tax-free, both for the employer and the worker.

"Our aim is to remove inequities in our tax laws and make tax relief for health insurance available to everyone," Martinez said.

The legislation would offer special tax credits to help cover the cost of health insurance and other health bills: $2,160 per person, up to a maximum of $5,400 per family.

Burr, a member of the Senate health committee, said the plan would level the field, describing a Robin Hood-like bureaucracy that would take money from those with rich health care plans to help pay for those who have nothing.

"Millions of Americans who are currently uninsured would have access to coverage in the free market," Burr said. He said the plan would give patients "buying power" by allowing them to hunt for personalized coverage.

He said the tax credit would cover an employment family health benefit worth up to $15,000.

"That's a pretty generous benefit," Burr said.

The legislation, called the Every American Insured Health Act, comes amid debate this week in the House of Representatives and the Senate over the renewal of a state-run children's health insurance program. Republican leaders, including President Bush, want to keep the program as is.

Democrats, however, are trying to expand the program to cover more children.

The GOP legislation also comes as the idea of universal health care continues to consume political debate. Polls show health care as one of the top concerns of voters. Democratic presidential candidates are being pushed to unveil their health care plans. And several states are considering legislation to cover uninsured residents.

Burr said GOP leaders asked him and a handful of other Republicans to develop an alternative to the children's health program.

After working for several months on the bill, he said, the group decided "not to try to fit a round peg into a square hole" and came up with a different idea entirely.

Coburn said the proposed children's health program expansion amounts to more bureaucrat-controlled health care.

"Rather than forcing our children to board a sinking ship, we can allow all Americans to buy their own boat," Coburn said.

But Kathleen Stoll, director of health policy for Families USA, an advocacy group in Washington, said the idea isn't terribly new. Republicans have long been working to dismantle the employment-based health system that most Americans now use, she said.

"When we eliminate that tax break for (the system), we should do that with extreme caution," said Stoll, who hadn't seen the legislation because it hadn't been filed.

Advocates for the uninsured fear that employers could drop health benefits altogether. And for many families, $5,400 won't buy a lot of health insurance.