JOHNSTON - Iowa Sen. Tom Harkin said Friday his prediction that a sweeping overhaul of the country's health care system would pass this year was too optimistic, but he remains confident Congress will approve the landmark changes.

''I had been predicting all year that we would have a bill on the president's desk by Christmas, but I think I'm a little off on that,'' Harkin said. ''We'll have a bill on the president's desk by the end of January.''

The five-term Democrat has had a key role in the health care debate since becoming chairman of the Senate Health, Education and Labor Committee. He took over that position after the August death of Sen. Edward Kennedy.

Harkin spoke during a taping of the Iowa Public Television program ''Iowa Press.''

Much of the criticism of the health care overhaul has focused on plans for optional government-run health coverage for people who do not have insurance through their current employers.

Opponents have pushed hard against the so-called public option, especially during summer rallies and town hall meetings where some argued it amounted to a government takeover of the nation's health care system

Although national polls on the issue vary widely, Harkin said he thinks the politics of health care reform are simple and that most Americans want Congress to act.

''The public option is going to be in the bill. We are going to have a very strong public option,'' said Harkin. ''The politics are very clear. By almost 2-to-1 the American people want a public option in health care as a choice.''

Harkin said Democrats and physicians support a public option by even wider margins.

''Among Democrats it's 4-to-1,'' said Harkin. ''Among doctors in the United States, 3-to-1 say we have to have a public option. The American people want this.''

Harkin said there's growing momentum for a health care bill, noting the endorsements Thursday by the seniors' lobbying group AARP and the American Medical Association.

''Many of the Republicans argue that we are going to harm Medicare,'' said Harkin. ''If AARP is endorsing it, I rather doubt that argument will hold much water.''

Other argue that effort will put a government bureaucrat between patients and doctors.

''If that were true I doubt the American Medical Association would be endorsing this bill,'' said Harkin.