Some firefighters have told officials that they never heard an evacuation order after the second plane hit Sept. 11, The New York Times and the Daily News reported. As a result, they said, they did not know that Chief Joseph Callan had broadcast a message over the radios in which he ordered the firefighters to "come down to the lobby," the Times said.

Deputy Chief Peter Hayden, who was in charge of the command post in the north tower lobby, told the Daily News, "There were companies as high as the 50th floor, and we weren't able to communicate with them to come down."

A spokesman for the department, Francis X. Gribbon, told the Times that investigators had not determined whether the reported problem resulted from a breakdown in reception or transmission or whether some other factor may have prevented some firefighters from hearing the command.

"Some people heard it and some people didn't," he said. "We're doing an investigation and when we get everyone's testimony we hope to have a comprehensive idea of just what happened."

The Daily News reported that the problem with the Motorola two-way radios functioning in high-rises was well known, and a special booster system was installed at the World Trade Center after the 1993 bombing there.

But the booster system was knocked out during the Sept. 11 attack, Port Authority spokesman Allen Morrison said. It relied on a 3-foot antenna atop 5 World Trade Center, which was taken out by falling debris.

The Fire Department has already interviewed more than 300 people to get a better sense of how the fire companies responded on the day of the attack and what problems they encountered. Among those interviewed have been 135 fire officers or firefighters. Gribbon said it was unclear how many of those interviewed had indicated that they had a problem hearing the order.

Officials have estimated that several hundred firefighters had rushed into each of the towers and worked there successfully to evacuate some 25,000 people before the towers fell.