In opening remarks, Mr. Giuliani said the city's police and firefighters were heroes for their efforts to evacuate people after two hijacked airplanes slammed into the twin towers of the World Trade Center.

He said the evacuation efforts helped save another 8,000 people who could have died in the terrorist attacks.

Later Wednesday, Mr. Giuliani's successor Michael Bloomberg and U.S. Homeland Security Secretary Tom Ridge are also due to appear before the commission in New York.

Tuesday, the commission said a lack of communication hampered rescue efforts at the World Trade Center.

In a report, the commission was largely sympathetic to the difficulties police and firefighters inside the twin 110-story towers. But the report noted that emergency line phone operators had a "lack of awareness" of what was happening as people inside the burning buildings called and asked for help.