President Bush (search) on Sunday marked the fourth anniversary of the Sept. 11 (search) terrorist attacks by observing a moment of silence at 8:46 a.m., the exact minute in 2001 when terrorists smashed the first jetliner into the World Trade Center.

The president stood with his wife, Laura (search), and Dick and Lynne Cheney on the South Lawn during the simple ceremony that has been repeated each year since the attack.

All four wore dark suits and held their hands over their hearts, facing south to the Washington Monument, as a bugler played taps. Bush did not speak, and the only other sound was the roar of jet planes landing and taking off at nearby Reagan Washington National Airport (search) in an unscripted yet eerie reminder of the attacks.

The flag on top of the White House flew at half staff, as it has for the past week in honor of the victims of Hurricane Katrina (search).

Scores of administration and White House staff, including Cabinet members, policy advisers, interns, maintenance men and kitchen crews, stood behind the Bushes and Cheneys with eyes closed in prayer. Among them were Defense Secretary Donald H. Rumsfeld and Homeland Security Secretary Michael Chertoff.

The Bushes, the vice president and his wife, and several Cabinet members began the day at a prayer service at St. John's Episcopal Church on Lafayette Park across from the White House. They joined the congregation in reciting prayers for the victims and survivors of Sept. 11 and the hurricane.

The Rev. Luis Leon preached that the anniversary was a time for healing and forgiveness and said the attacks have inspired a new generation to become more politically active. "If they ever wondered why they should bother to vote, then 9-11 and certainly now Katrina gave them an answer," Leon said.

Later, the president was to fly to New Orleans and spend the night in the hurricane-devastated city. On Monday, he planned to tour Gulfport, Miss.