President Obama’s ability to shape the debate on health care appears to be eroding as opponents aggressively portray his overhaul plan as a government takeover that could limit Americans’ ability to choose their doctors and course of treatment, according to the latest New York Times/CBS News poll.

Americans are concerned that revamping the health care system would reduce the quality of their care, increase their out-of-pocket health costs and tax bills, and limit their options in choosing doctors, treatments and tests, the poll found. The percentage who describe health care costs as a serious threat to the American economy  a central argument made by Mr. Obama  has dropped over the past month.

Mr. Obama continues to benefit from strong support for the basic goal of revamping the health care system, and he is seen as far more likely than Congressional Republicans to have the best ideas to accomplish that. But reflecting a problem that has hindered efforts to bring major changes to health care for decades, Americans expressed considerable unease about what the end result would mean for them individually.

“We need to fix health care,” Mary Bevering, a Democrat from Fort Madison, Iowa, said in a follow-up interview, “but if the government creates the system, I’m afraid the quality of care will go down and costs will go up: We will pay more taxes.”