WASHINGTON — The Bush administration has counted on growing public appreciation of a strong economy to bolster Republican prospects in fall congressional races. That has not materialized, and the economy may have peaked months before the election.

The public is divided over whether the economy is doing well, a new Bloomberg/Los Angeles Times poll suggests, with a strong majority giving President Bush and the Republicans negative marks on the issue.

“It wasn’t long ago that the president was crowing about the economy’s strength,” the publisher of the Washington-based Rothenberg Political Report, Stuart Rothenberg, said. “Now it’s hard to see the economy helping the president turn around his unimpressive poll numbers. The public is unhappy, and they’re likely to take that out on Republicans running for the House and Senate.”

Almost three out of five Americans disapprove of the way Mr. Bush is handling the economy, the poll shows. Economic growth is forecast to slow to an annual pace of less than 3% in the second half of this year, from an average of about 4% in the first half, according to a Bloomberg survey of economists.

The 56-month expansion is the fourth longest since World War II. The economy has generated 5.4 million new jobs since June 2003, and the unemployment rate has dropped to 4.6%, a level economists consider full employment.

Yet many Americans remain unimpressed, the poll shows.

Fewer than one in 10 respondents said the economy is doing very well, and slightly more than four in 10 said fairly well. Almost half said the economy is doing badly, including 21% of those who identified themselves as Republicans. The proportion of Americans who disapprove of Mr. Bush’s handling of the economy rose over the last month, to 59% from 54% in June.

“Bush could be doing a better job,” Meredith Rice of Choctaw, Okla., said. The 34-year-old patient services representative, who considers herself an independent voter, points to gasoline prices and the cost of the war in Iraq. “Bush is letting things here slip,” Ms. Rice, one of several poll respondents contacted for a follow-up interview, said.

More than twice as many Americans think things in America are seriously on the wrong track as those who said they are going in the right direction. A third of Republicans said the country is on the wrong track.

The poll of 1,478 adults, including 1,331 registered voters, was taken between July 28 and August 1, and both samples have a margin of error of three percentage points. Thirty-nine percent of those surveyed identified themselves as Democrats, 35% as Republicans, and 25% as independents or another affiliation.

The survey may spell trouble for the Republican Party as it seeks to maintain its control of Congress. Republicans hold 231 seats in the House of Representatives, where all 435 seats are up for grabs this year, and 55 seats in the Senate, where a third of the 100 seats are being contested.

Registered voters favor Democrats over Republicans in congressional contests by a margin of 48% to 37%, the poll suggests.

The attitudes of swing voters, including middle-income Americans and independents, are more troublesome still for the Republican Party.

Independent voters take a much more negative view of the economy than the overall sample, with six in 10 saying it is doing badly and almost two-thirds disapproving of Mr. Bush’s handling of it. By a margin of 70% to 24%, independents said the country is on the wrong track.

Affluent Americans are more positive about the nation’s direction and Mr. Bush’s economic leadership. Sixty-five percent of respondents with incomes above $100,000 said the economy is doing well, compared with 45% of those with household incomes under $40,000 who hold that view.

Only a quarter of those in the lower income category said the nation is going in the right direction. That increases to 43% in the higher bracket. And while almost half of the wealthier group approves of the way Mr. Bush is handling the economy, less than a third of the lower income group does.

Americans are feeling the pain of higher costs for gasoline and electricity. Three of four respondents said they have been forced to conserve energy, cut back on other spending, or both.

About six in 10 Americans disapprove of Mr. Bush’s veto last month of legislation passed by the Republican-controlled Congress that would have eased limits on federal funding for research on new embryonic stem cells.