The poll, conducted Sept. 6-9 with 938 respondents, found 77 percent of those living in the East and 46 percent of those living in the West -- 61 percent overall -- said they think about the attacks at least weekly. Eighty-one percent -- 90 percent in the East and 75 percent in the West -- said the attacks were the most significant historical events of their lives.

Tuesday marks the sixth anniversary of the day terrorists hijacked four commercial airliners, flew two into the World Trade Center in New York and one into the Pentagon in Washington. The fourth crashed in a field in Pennsylvania as passengers prevented the hijackers from heading for their target in Washington.

Some 83 percent said they think the nation should remember the attacks with some formality and 16 percent said they had visited Ground Zero.

Sixty-two percent said the nation is better protected now than it was on Sept. 11, 2001, while 14 percent said it was less well-protected. And 91 percent said they believe another attack is inevitable, possibly against the nation's food or water (20 percent). Seventeen percent said they expected terrorists to launch a poison or disease attack while 16 percent predicted a car bomb.

The poll had an error margin of 3.3 percentage points.