Former New York mayor Rudolph W. Giuliani acknowledged Wednesday that some "terrible mistakes" were made in the immediate response to the Sept. 11, 2001, attack on the World Trade Center, but he gently suggested that the national commission investigating the tragedy should focus on the future rather than on apportioning blame for the past.

Giuliani appeared to be responding to criticism leveled by the panel at communications difficulties and organizational problems encountered by his former police and fire chiefs during the rescue effort.

"We're all hurt. We're all very, very angry," Giuliani said during the second day of hearings in New York by the Sept. 11 commission. "We're all feeling the loss of heroes we all love . . ."

But "we have to channel our anger to do all we can" to prevent future attacks and improve the responses to them, he added.

"Our enemy is not each other, but the terrorists who attacked us," Giuliani said softly and without anger in his opening statement to the panel. "The blame should clearly be directed at one source and one source alone, the terrorists who killed our loved ones," Giuliani said.

"Maybe 8,000 more, maybe 9,000 more than anyone could rightfully expect" were evacuated safely from the World Trade Center that day, he said.

Giuliani was the first witness at Wednesday's hearing in Greenwich Village, about 1 1/2 miles from Ground Zero. The panel, formally known as the National Commission on Terrorist Attacks Upon the United States, was created by Congress to examine what led to the attacks and advise ways the country can avoid and respond to future attacks.

The former mayor, hailed internationally for his commanding performance during the emergency, then recounted to a rapt commission his own experience on that day as he began to realize the gravity of the attack.

Summoned from a routine breakfast, Giuliani said he reached the scene shortly after it occurred along with the police commissioner.

The two looked upward and saw what they thought was debris falling from one of the twin towers of the World Trade Center.

He then realized "it was a man throwing himself off the 102d or 103d floor. I was in shock. I turned to the commissioner and said 'we're in uncharted territory. We've never done anything like this before . . . We're just going to have to stay together.' "

The two, along with other top emergency response officials, then gathered at an outdoor command center where they could see both towers. "That was typically the way you fight fires. We had a board in front of us . . . making an attempt to figure out where resources are located."

"My first question" to the fire chief was "can we get helicopters to the roof. I could see people hanging out the windows. I thought I saw people on the roof. I didn't," as it turned out, he recounted.

The fire chief "pointed to a big flame that was shooting out of the North Tower at the time. He said to me, 'My guys could save everybody below the fire. But I can't put a helicopter near there. The helicopter would blow.' "

The concern of the police and fire chiefs were "to get people out of the area. . . . You could see that things were falling off the building and hitting people and you could see bodies falling down. . . . I told him I was going to communicate this to everyone and be back. I shook his hand. I said, 'God bless you.' He said the same."

Giuliani then got his deputy mayors and other emergency officials together at an indoor makeshift command post on West Street, near the Twin Towers. At that point, he said, he had heard there were seven planes unaccounted for and feared that other targets would be hit. He called the White House and was told that jet fighters were on there way and that Vice President Cheney was about to phone him.

Moments later, "I got a call from the White House operator. She said the vice president would be on in a moment." Then, he continued, "I heard a click. The desk started to shake." He said he heard an aide say, "The tower is down. The tower is down."

"My first thought was that one of the radio towers had come down. But I could see the desk shaking. I could see people in the outer office going under desks and could see outside a tremendous amount of debris," said the former mayor.

"It felt like an earthquake and then looked like a nuclear explosion. . . .

"We went down into the basement. We had to get everyone out of the building."

Giuliani said they went from door to door and found them all blocked, apparently by debris in the streets. Finally, he ran into two janitors, who showed them a way out through the basement."

As they emerged with "a sigh of relief," he said, they then saw "a tremendous cloud. There was debris flying through the street and people were being injured."

He then made a decision to stay outside for fear that the building he had been in would collapse, "destroying" the "whole city government," the mayor, two deputy mayors, the commissioner of public health and the head of emergency services, who had by then joined him.

"What I saw was very inspiring," Giuliani told the commission. "I didn't see people knocking each other over . . . I saw acts of people helping each other. Somebody would fall down and someone would pick them up."

Then, he recalled, "we heard a tremendous noise. . . . The second building had come down. I saw the cloud from the second building come up the streets."

The mayor and his group then headed for the New York police academy to use as a new command center, as it was equipped with communications equipment. From there, he said he contacted New York Gov. George E. Pataki, who dispatched the National Guard to the city.

"I had always resisted having the National Guard. New York City is difficult enough to police . . . That isn't what they do. But we were in such need, I said yes."

Giuliani's testimony before the Sept. 11 commission was interrupted with angry outbursts by victims' families, with one yelling "One-sided!" and "Put us on the panel!"

"My son was murdered!" yelled a woman identified by the Associated Press as Sally Regenhard, who lost her firefighter son in the attack. Others in the audience shouted about the failure of Fire Department radios, shouting, "Talk about the radios!"

"You're simply wasting time at this point," commission chairman Thomas H. Kean, a Republican former governor of New Jersey, told the family members.

"You're wasting time!" came the angry reply.

Earlier Wednesday, the commission released another report about New York's response to the Sept. 11 attacks. It said that in the crucial minutes following them, fire officials failed to realize that they could dispatch firefighters more quickly to the South Tower of the World Trade Center, which may have reduced the number of people trapped inside when the tower fell.

The North Tower had been hit by American Airlines Flight 11 at 8:46 a.m. United Airlines flight 175 slammed into the South Tower 17 minutes later.

Because of a lack of timely information after the second airplane hit, commanders dispatched new fire units to the South Tower instead of turning to units on hand in the North Tower.

As a result, the additional firefighters arrived later and, in many cases, were killed in the ensuing collapse of the South Tower at 9:59 a.m., the report said.

"If they had understood that units were still arriving at the North Tower or were already there but still in the lobby, they could have considered whether to reassign some of the units already at the scene to render immediate assistance in the South Tower," the staff wrote in an eight-page report.

"The decision to handle the South Tower by dispatching new units meant that the number of firefighters available to help evacuees in that tower was relatively small for at least the first 20 minutes after the tower was hit, though that number sadly was rising in the minutes before that tower collapsed."

This haunting conclusion is part of the latest report to be released by the commission. By contrast, the report found that the emergency response to the attack on the Pentagon in Northern Virginia was "mainly a success," in large part because the Washington region and federal government had in place a clear command system that vested a significant amount of power in one entity: the Arlington County Fire Department. The county's fire chief, Edward P. Plaugher, is also slated to testify today.

But the commission report also cautioned that the "two experiences are not comparable" because of the sheer scale of the calamity at the World Trade Center, which, unlike the Pentagon, involved tens of thousands of potential victims and was far less contained.

The staff also found that authorities in the Washington area reported communication glitches and other problems that were similar to those reported by their New York City counterparts. In an "after-action report" by Arlington County, for example, officials described many of the same problems with radio channels and equipment that plagued firefighters and police at the World Trade Center.

"Almost all aspects of communications continue to be problematic, from initial notification to tactical operations," the Arlington report said, according to the commission. "Cellular telephones were of little value . . . . Radio channels were initially oversaturated . . . Pagers seemed to be the most reliable means of notification when available and used, but most firefighters are not issued pagers."

The commission's report concluded that "it is a fair inference, given the differing situations in New York City and Northern Virginia, that the problems in command, control, and communications that occurred at both sites will likely recur in any emergency of similar scale. The task looking forward is to enable first responders to respond in a coordinated manner with the best situational awareness possible."

The report recommends that New York adopt an "incident command" system to provide better coordination and control during major emergencies. Although New York officials testified Tuesday that a plan released by Mayor Michael Bloomberg last week fits that definition, several commission members argued it may cause more problems than it solves.

John F. Lehman, a Republican former Navy secretary, called New York's response system "dysfunctional" and said it was "not worthy of the Boy Scouts, let alone this great city."

Barbash reported from Washington.