Obama's favorability rating among Democratic primary voters dropped 7 percentage points to 62 percent since the last survey in late February, the Times said. The decline has been mostly among men and upper-income voters.

Since the last survey, the Illinois senator has been fighting off attacks from rival New York Sen. Hillary Clinton.

Obama also gave a speech on race last month in response to reports that his former pastor had made racially charged and anti-American statements at his Chicago church.

Obama's big lead among men over Clinton disappeared during that period, the Times said.

In February, 67 percent of men wanted the Democrats to nominate Obama compared with 28 percent for Clinton. Now, 47 percent of men back Obama compared with 42 percent for Clinton, the poll found.

Obama's lead among whites, voters making more than $50,000 annually and voters under age 45 has also shrunk, The New York Times reported.

Ahead of the April 22 Pennsylvania primary, Clinton and Obama are effectively tied among Democratic voters nationwide.

According to the poll 46 percent want Obama to be the party's nominee compared with 43 percent who prefer Clinton.

The survey has a margin of error of plus or minus 3 percentage points for all voters, 4 percentage points for Democratic primary voters and 5 percentage points for Republican primary voters.

The poll suggests presumptive Republican nominee John McCain is enjoying some success as the Democratic candidates remain locked in a contentious fight for the nomination to face him in the November election, the Times reported.

McCain is now viewed positively by 67 percent of Republican primary voters, compared with 57 percent in February.

In matchups with McCain, Obama leads by 47 percent to 42 percent, and Clinton also holds a 5-point lead over the Arizona senator, 48 percent to 43 percent, the survey found.

In late February, before McCain clinched his party's nomination, Obama led the Republican contender 50 percent to 38 percent.