The voices of two Sept. 11, 2001, hijackers participating in the attacks were revealed publicly for the first time yesterday, when the commission investigating the terrorist strikes played recordings of their instructions to passengers shortly after two aircraft were commandeered.

The terrorists' remarks had been cited in news reports but never before played publicly.

At 8:24 a.m. on Sept. 11, an air controller in Boston received the following transmission from American Airlines Flight 11, which had taken off from Boston's Logan International Airport 24 minutes earlier. The voice is believed to belong to the ringleader of the 19 terrorists, Mohamed Atta, but the commission did not identify the speaker in the report it released yesterday or at yesterday's public hearing.

"We have some planes. Just stay quiet and you'll be okay. We are returning to the airport."

According to the commission's report, the controller did not hear the whole statement. But seconds later, another transmission followed.

"Nobody move. Everything will be okay. If you try to make any moves, you'll endanger yourself and the airplane. Just stay quiet."

At 8:34, the Boston air controller received a third transmission from the plane. "Nobody move, please. We are going back to the airport. Don't try to make any stupid moves."

The jetliner crashed into the World Trade Center's North Tower at 8:46 a.m.

Just under an hour later, about 9:29 a.m., a Cleveland air controller monitoring United Airlines Flight 93 from Newark heard "a radio transmission of unintelligible sounds of possible screaming or a struggle from an unknown origin," the report says. A second transmission soon followed; the controller heard screaming and someone yelling, "Get out of here, get out of here."

The controller unsuccessfully tried to contact the plane and polled other pilots who said they had heard the screaming. A third transmission, received at 9:32, was a voice saying: "Keep remaining sitting. We have a bomb on board."

The commission played aloud a transmission received at 9:39 that is attributed to Ziad Samir Jarrah, who was believed to be piloting the plane.

"Uh, is the captain. Would like you all to remain seated. There is a bomb on board and are going back to the airport, and to have our demands [unintelligible]. Please remain quiet."

Flight 93 crashed in rural Shanksville, Pa., at 10:03 a.m.

Mohamed Atta, a hijacker on American Flight 11: "Don't try to make any stupid moves."Ziad Samir Jarrah, on United Flight 93: "There is a bomb on board. . . . Please remain quiet."