Yet, polls capture only a particular moment in time, and can be influenced by the way questions are asked or the mix of people who are surveyed. In The Times/CBS News poll, the margin of sampling error could mean the president’s approval rating is as high as 44 percent or as low as 38 percent, at a 95 percent confidence level. The telephone poll was conducted March 7 to 11 with 1,009 adults nationwide.

Mr. Obama’s aides have expressed concern for weeks that rising gas and fuel prices and outside forces like the turmoil overseas or a spike in unemployment could harm his political standing.

The decline in Mr. Obama’s approval rating has occurred as Americans are confronted by rising gas prices on filling station billboards and the evening news. Republican presidential candidates have sometimes tried to connect the price increases to the Obama administration’s approach to Iran.

Mr. Obama’s drop was particularly pronounced among low-income households that may be feeling the pinch of the higher gas prices — as well as increases in prices for groceries and some retail items — more than others.

Over all, 54 percent of poll respondents believed that a president can do a lot to control gas prices, as opposed to 36 percent who believe they are beyond a president’s control.

“I think just being the president of the United States of America, you would have some type of control over gas pricing,” said Jamie Haber, 39, an independent voter of Orlando, who voted for Mr. Obama in 2008 but says he will not this year. “We’re out here doing everything we can to make a living, and gas prices keep going up,” he said in a follow-up interview.

While the Republican candidates for president have for the most part been united in their criticism of Mr. Obama over his handling of Iran, the public is more or less evenly divided on his approach, the poll found, with 42 percent approving and 39 percent disapproving.