Speaking at a briefing about the World Trade Center disaster, Police Commissioner Bernard Kerik also said five or six people, some of them Arab nationals, were detained at the city's airports for questioning by the FBI and the Joint Terrorist Task Force.

The region's three major airports - Kennedy, La Guardia and Newark, N.J. - were opened briefly for the first time since Tuesday's disaster and then abruptly closed. Kerik did not indicate whether the closings were related to the arrest or detentions.

In a city clearly rattled two days after the attacks, more than 90 false bomb threats were investigated in Manhattan before noon, Mayor Rudolph Giuliani said.

''We're going to try to catch the people who are making these threats, and the governor suggested we make an example of them,'' he said.