The Sept. 11 commission, in bitter exchanges with former top New York City officials Tueday sharply criticized parts of the response to the attack on the World Trade Center, citing poor communication and bad preparation.

A report released Tuesday portrayed 100 minutes of chaos and confusion between when the north tower was hit in the first strike and its collapse after the south tower fell:

Trade center tenants, inadequately prepared for a disaster, didn't know what to do and couldn't get information from 911 operators they called.

Police and firefighters, historic and sometimes bitter rivals, set up separate command posts and had difficulty communicating between and among their agencies. Nearly 20 minutes before the north tower collapsed at 10:26 a.m., a police helicopter hovering near the top advised it wouldn't last much longer, but "there was no way to relay this information to the fire chiefs in the north tower."

Commissioner John Lehman, a former Navy secretary, excoriated the city's former public-safety chiefs for not having better cooperation and communications equipment. "The command and control and communications of this city's public safety is a scandal," Lehman said to applause from a crowd of 400 that jammed an auditorium at New School University in lower Manhattan. "It's not worthy of the Boy Scouts let alone this great city."

"I think it's outrageous of you to make a statement like that," former fire commissioner Thomas Von Essen shot back, eliciting cheers of his own. Other former city officials said they communicated well in overwhelming circumstances.

Commission investigators zeroed in on a confusing 17-minute span between when the towers were struck, as people in the south tower, hit second, received contradictory instructions about whether to evacuate. The south tower's public-address system told people to stay and return to their offices, apparently to avoid going outside and getting hit by debris and people falling from the north tower.

Minutes later, fire officials ordered the south tower evacuated, but a Port Authority police commander issued the command over a radio channel that could be heard only by some Port Authority police and not other agencies. When United Airlines Flight 175 hit the tower around the 78th floor, hundreds of people had been waiting there to evacuate. Many were killed or seriously injured, commission investigators said.

In the north tower, chiefs ordered an evacuation, which many firefighters didn't hear because their radios channel was overwhelmed, they were listening to the wrong channel or they had been off-duty and didn't have their radios. The evacuation order did not include a "mayday" call and firefighters who heard it "lacked a uniform sense of urgency," the commission said.

The commission took aim at the Port Authority of New York and New Jersey, which built the trade center, operated it until shortly before Sept. 11, 2001, yet had no plan to rescue people trapped above a fire. Even as it improved emergency procedures after the center was bombed in 1993, the Port Authority evacuation drills didn't direct tenants to stairwells, didn't tell them about stairway configurations, which were confusing, or that they couldn't get to the roof, which many attempted hoping to be rescued by helicopter, as a dozen were in 1993.

"Most civilians recall simply being taught to await instructions which would be provided at the time of an emergency," the commission stated in a 26-page report.

Under sharp questioning, Alan Reiss, the Port Authority official in charge of the trade center in 2001, admitted, "You're right, we didn't have people walk down 50 flights of stairs. That may be something we need to do -- people need to understand what they'll encounter."

In a new twist on criticism of communications, the commission cited 911 operators for providing little help to frantic callers in the north tower, who couldn't hear evacuation orders over the public-address system, which American Airlines Flight 11 had knocked out.

Emergency operators "had no information" about where the plane hit the building and couldn't tell callers if they were above or below the impact area, which might have suggested whether they should try to walk down stairs. The operators also got no information that rooftop rescues were impossible and told callers both above and below the impact zones to stay put and wait for emergency personnel.

Commission investigators played on a large screen a videotaped interview of Brian Clark, who worked in the north tower and recalled being put on hold twice by 911 operators who said he needed to talk to a supervisor as he tried to alert them to an injured person on the 44th floor.

Slade Gorton, a Republican commissioner, seemed incredulous as he pressed former police commissioner Bernard Kerik on why the supervisor at the 911 emergency-call center, run by the Police Department, didn't also listen to Fire Department communications to inform operators who could pass information on to callers.

"Whether he listened to the Fire Department radio I cannot say," Kerik replied. "That may be the case."

As it added new criticisms, the commission also quelled old ones, such as the absence of roof evacuation. The commission suggested that was impossible because the roof doors were locked for safety reasons and intense smoke and heat made flying helicopters difficult.

And the commission noted that although 2,749 people died at the trade center, including 343 firefighters, 25,000 were saved. While many firefighters didn't hear orders to leave the north tower, the commission report said, many did but chose to "delay their evacuation in order to assist victims who could not move on their own."