Washington ? At the very moment when President Barack Obama is looking to thrust the U.S. ever more into global affairs, from Afghanistan to climate change, the American public is turning more isolationist and unilateralist than it has at any time in decades, according to a new poll released Thursday.

The survey by the Pew Research Center found a plurality of Americans — 49 percent — think that the U.S. should “mind its own business internationally” and leave it to other countries to fend for themselves.

It was the first time in more than 40 years of polling that the ranks of Americans with isolationist sentiment outnumbered those with a more international outlook, Pew said.

“The U.S. public is turning decidedly inward,” Pew said.

The U.S. is also growing more unilateralist, with 44 percent saying that the U.S. “should go our own way in international matters, not worrying about whether other countries agree with us or not.”

That was the highest percentage since the question was first asked in 1964.

The country also has grown pessimistic about U.S. clout in world affairs.

By a margin of 41 percent to 25 percent, Americans think the U.S. is playing a less important role in the world than 10 years ago. It was the first time since the 1970s — when the U.S. had withdrawn from Vietnam, been hurt by an Arab oil embargo and seen its citizens held hostage in Iran — that a plurality of Americans thought their country was weaker than it had been a decade before.

The shift in sentiment comes after more than eight years of war in Afghanistan and almost seven in Iraq, and in the midst of the worst economy since the Great Depression.

Just 32 percent of the public favors increasing U.S. troops in Afghanistan, and only 46 percent say it’s likely that Afghanistan will be able to withstand the threat posed by the Taliban.

The survey of 2,000 U.S. adults was taken from Oct. 28-Nov. 8 — before Obama’s speech on Afghanistan on Tuesday night. It has an error margin of plus or minus 3 percentage points.