Almost half, 49 percent, told the polling organization that the United States should "mind its own business" internationally and let other countries get along the best they can on their own, the Pew Research Center survey found. That's up from 30 percent who said that in December 2002.
Results of the survey appear to conflict with President Barack Obama's activist foreign policy, including a newly announced buildup of 30,000 U.S. troops in Afghanistan to fight Taliban and al Qaeda extremists.
"Isolationist Sentiment Surges to Four-Decade High," the nonpartisan research center headlined its report on the poll about America's role in the world.
Only 32 percent of the poll respondents favored increasing U.S. troops in Afghanistan, while 40 percent favored decreasing them. And fewer than half, or 46 percent, of those polled said it was somewhat or very likely that Afghanistan would be able to withstand the radicals' threat.
Forty-one percent of those surveyed said the United States plays a less important and powerful role as a world leader than it did a decade ago, up from 25 percent who said that just before the Sept. 11, 2001, terrorist attacks, the report said.
Pew Research Center President Andrew Kohut said in an interview that the "very bad economy" appeared most responsible for the growth of isolationist sentiment. He said the public was also "displeased with the two wars we are waging, in Iraq and Afghanistan."
"Improving human rights and living standards are all down," Kohut added Thursday at a news conference.
"It tells us the president is sailing into a stiff wind," said James M. Lindsay, director of studies at the private Council on Foreign Relations.
"Unless he can produce obvious successes in Afghanistan and generally, he will find himself challenged," Lindsay said.
Nearly half the public worried the president is not tough enough in defending interests of the U.S. generally, Lindsay said.
While isolationism and unilateralism reached four-decade highs among the public, the stature of China increased.
Among Americans polled, 44 percent said China was the world's leading economic power, compared with 27 percent who named the United States. In February 2008, 41 percent said the U.S. was the leading economic power, while 30 percent said China was.
A majority of Americans surveyed, or 53 percent, see China's emerging power as a threat to the United States.
The United States is seen by a comfortable majority, 63 percent, as the world's leading military power.
Concerning the Middle East, about half, or 51 percent, of respondents said they were more sympathetic toward Israel than to the Palestinians, who drew 12 percent. Fourteen percent supported neither side, while 19 percent offered no opinion.
The findings come from two surveys. The first poll, of 2,000 adults, was conducted by telephone Oct. 28 to Nov. 8 and had a margin of sampling error of plus or minus 3 percentage points. A subsequent poll of 1,003 people conducted from Nov. 12-15 had a margin of error of plus or minus 4 percentage points.