Washington ? It’s the cost, Mr. President.

Americans are worried about hidden costs in the fine print of health care overhaul legislation, an Associated Press poll says. That’s creating new challenges for President Barack Obama as he tries to close the deal with a handful of Democratic doubters in the Senate.

Although Americans share a conviction that major health care changes are needed, Democratic bills that extend coverage to the uninsured and try to hold down medical costs get no better than a lukewarm reception.

The poll found that 43 percent oppose the health care plans being discussed in Congress, while 41 percent are in support. An additional 15 percent remain neutral or undecided.

“Well, for one, I know nobody wants to pay taxes for anybody else to go to the doctor — I don’t,” said Kate Kuhn, 20, of Acworth, Ga. “I don’t want to pay for somebody to use my money that I could be using for myself.”

There’s been little change in broad public sentiment about the overhaul plan from a 40-40 split in an AP poll last month, but not everyone’s opinion is at the same intensity. Opponents have stronger feelings than do supporters. Seniors remain more skeptical than younger generations.

The latest survey was conducted by Stanford University with the nonprofit Robert Wood Johnson Foundation.

When poll questions were framed broadly, the answers seemed to indicate ample support for Obama’s goals. When required trade-offs were brought into the equation, opinions shifted — sometimes dramatically.

In one striking finding, the poll indicated that public support for banning insurance practices that discriminate against those in poor health may not be as solid as it seems.

A ban on denial of coverage because of pre-existing medical problems has been one of the most popular consumer protections in the health care debate. Some 82 percent said they favored the ban, according to a Pew Research Center poll in October.

In the AP poll, when told that such a ban would probably cause most people to pay more for health insurance, 43 percent said they would still support doing away with pre-existing condition denials, but 31 percent said they would oppose it.

Costs for those with coverage could go up because people in poor health who’d been shut out of the insurance pool would now be included, and they would get medical care they could not access before.

“I’m thinking we’d probably pay more because we would probably be paying for those that are not paying. So they got to get the money from somewhere. Basically I see our taxes going up,” said Antoinette Gates, 57, of Atlanta.

The health care debate is full of such trade-offs. For example, limiting the premiums that insurance companies can charge 50-year-olds means that 20-year-olds have to pay more for coverage.

“These trade-offs really matter,” says Robert Blendon, a professor at the Harvard School of Public Health who follows opinion trends. “The legislation contains a number of features that polls have shown to be popular, but support for the overall legislation is less than might be expected because people are worried there are details about these bills that could raise their families’ costs.”

If the added costs — spread over tens of millions of people — turn out to be small, it may not make much difference, Blendon said. But if they’re significant, Obama could be on shaky ground in the final stretch of his drive to deliver access to health insurance to most Americans.