Illinois Sen. Obama leads McCain by 12 percentage points -- 52 percent to 40 percent; New York Sen. Clinton leads McCain by 6 points -- 50 percent to 44 percent, the poll found.

McCain, an Arizona senator, has turned his attention to the the Nov. 4 general election after clinching his party's nomination on Tuesday night. Clinton and Obama are still locked in a close battle for the Democratic nomination.

McCain, endorsed by U.S. President George W. Bush, fares poorly against Clinton and Obama among Americans who disapprove of the president and Americans opposing the war, The Washington Post said.

About two-thirds of Americans disapprove of the way Bush is handling his job and think the war was not worth fighting, the newspaper said.

Age might be another obstacle for 71-year-old McCain, who if elected would be the oldest first-term president.

The percentage of Americans discouraged by McCain's age (27 percent) is more than double the number who would be less enthusiastic about supporting Obama, who would be the first African American president or Clinton, who would be the first female president, the Post reported.

In a campaign pitting McCain against Obama, the veteran Arizona lawmaker pulls ahead of the junior senator from Illinois on the question of "experience." Sixty-eight percent of Americans who favor experience over "change" support McCain. However, 80 percent of those who desire a new direction and new ideas favor Obama, the poll found.

In a matchup with Clinton, the Republican holds a wide lead among those seeking experience while Clinton wins two-thirds of voters seeking change, the newspaper reported.

Obama also leads McCain on top issues in the poll: the economy, health care, immigration and ethics in government. The survey shows McCain with a wide advantage as the one better suited to handle the U.S. campaign against terrorism, the Post said.