Sirens screamed in the background as the callers pleaded for help. Although there were no voices, their desperation was evident in heavy, audible breathing on the other end of the operators' calls.

Glen Corbett, left, a professor of fire science at John Jay College, assists Rosemary Cain, center, and Barbara Hetzel as they listen to compact discs of emergency calls from Sept. 11, 2001, released in New York Friday March 31, 2006. [AP]

"If you feel like your life is in danger, do what you must do, OK?" one dispatcher told a caller at 9:02 a.m., just a minute before the second plane hit. "I can't give you any more advice than that."

The comment was typical of the frustration that came through amid the calm professionalism.

"All right, we have quite a few calls," said a fire operator.

"I know," said a police operator. "Jesus Christ."

Many dispatchers complained about computers failing in the chaos.

"Oh goodness. Hold on a second, because we are so backed up here," a fire dispatcher told one caller. "Because we have so much information on here, that our computers are down. OK?"

In the background of another call made from the 105th floor of the north tower at 9:17 a.m., a public address announcement could be heard in the background: "We aware of it down here. The condition seems to have subsided."

Sally Regenhard, one of the plaintiffs whose firefighter son was killed on Sept. 11, said the tapes showed that the operators were untrained to tell people how to save their lives.

"I'm hoping that the public and the system will learn how unprepared the City of New York and the Port Authority were on that day," Regenhard said.

Many of the operators told frantic callers to stay put and wait for help, which fire dispatcher supervisor David Rosenzwieg said is standard procedure in high-rises when fires break out on lower floors.

"Telling people to stay ¡ª for some reason people think that's the wrong thing to do," Rosenzwieg said Friday. "But the same instructions saves lives every day."

Rosenzwieg said some dispatchers were so traumatized by their encounters with the trade center victims they never came back to the job. Others retired early. "Unfortunately, they took it very much to heart," he said.

Police Commissioner Ray Kelly said the police 911 operators "displayed professionalism and compassion under the most trying of circumstances, often staying on the line with anguished callers until the very end."

At 9:47 a.m., one police operator did exactly that, telling another unidentified caller, "Yes, I'm here, I'm not going to go nowhere. ... You know there are people there trying to get you all out right now, all right? You're not by yourself."

The dispatcher then took a telephone number of the caller's family and promised to reach them. Then the call went dead: "And who is this? Hello?"

The first transcripts released as part of the Times lawsuit came last August, when thousands of pages of oral histories of firefighters and emergency workers, as well as radio transmissions, were released. The Port Authority of New York and New Jersey, which owned the trade center and has its own police force, released all its emergency recordings in 2003.

The Sept. 11 commission concluded in 2004 that the operators did not have enough information to allow more people to escape from the twin towers.

"Are they still standing?" one dispatcher asked at 10:15 a.m., 16 minutes after the south tower collapsed. "The World Trade Center is there, right?"