WASHINGTON - Aretha Franklin will sing, the Rev. Rick Warren will pray, and more than 11,000 U.S. troops will be watching over inauguration ceremonies in case of an attack during President-elect Barack Obama's swearing-in Jan. 20.

As many as four million visitors are expected to be on hand when Obama takes the noontime oath from Chief Justice John G. Roberts Jr. on the steps of the Capitol.

About 4,000 local police, 4,000 police from around the country, and security personnel from other government agencies will be on hand, taking direction from the Secret Service. About 7,500 active-duty military and 4,000 National Guard troops also will participate. That includes a contingent on alert to respond to a chemical attack.

Planners are working under the assumption a terrorist or rogue element might try to interrupt the event, said Gen. Gene Renuart, head of the U.S. Northern Command. "So it's prudent for us to plan for the possibility of that kind of event, and to be prepared either to deter it or to respond to it," he said.

Also yesterday, officials announced the list of participants for the inauguration.

The program is to feature poet Elizabeth Alexander; the Rev. Joseph Lowery, a veteran civil rights leader; the U.S. Marine and Navy bands; and the San Francisco Boys Chorus and the San Francisco Girls Chorus.

Sen. Dianne Feinstein (D., Calif.), who chairs the Joint Congressional Committee on Inaugural Ceremonies, said the day would be "an event of historic proportion."

"It is appropriate that the program will include some of the world's most gifted artists from a wide range of backgrounds and genres," she said.

Cellist Yo-Yo Ma, violinist Itzhak Perlman, pianist Gabriela Montero, and clarinetist Anthony McGill will perform a new work composed by John Williams, who also provided music for Obama's election-night rally in Chicago's Grant Park. Williams is best known for his film scores.

Vice President-elect Joseph R. Biden Jr. will take his oath from Justice John Paul Stevens.

Others on the schedule were a nod to Obama's election as the first black president. Lowery, who cofounded the Southern Christian Leadership Conference with the Rev. Dr. Martin Luther King Jr., is scheduled to offer the event's benediction.

Alexander, a 2005 Pulitzer Prize finalist and Yale University professor, centers her poems and essays on race relations and social movements.

Warren, popular among evangelicals, stayed publicly neutral during the presidential campaign. He invited Obama and Republican rival John McCain to his Saddleback Church in Orange County, Calif., for a forum on faith and public service.