It wasn't until he made an unexpected stop at Atlanta's Hartsfield International Airport more than two hours later that he learned the smoke was from the terrorist attack on the World Trade Center.

''I thought it was a fire,'' he said. ''We didn't hear anything until we got to Atlanta.''

Mr. Leitz was one of nearly 30,000 passengers at the airport affected by Tuesday's terrorist attacks in New York City and Washington.

Nearly 90 minutes after four commercial jets were hijacked and crashed, the Federal Aviation Administration ordered all traffic from the sky. That forced Mr. Leitz's flight to be diverted to Atlanta and other flights to be grounded.

Police officers with bomb-sniffing dogs and SWAT members patrolled all six of Atlanta's concourses after the massive facility was ordered closed. Roads leading into the airport were shut down, and signs around town flashed the message: ''National Emergency - Atlanta Airports Closed.''

The main terminal was clogged with stranded passengers who were desperately trying to find hotel rooms or rental cars. A counter for one rental car company had more than 300 people in line, although cars were sold out shortly after the airport's closure.

The wait for a taxi - the few that were allowed to breach the perimeter - was more than two hours.

Airport officials wouldn't disclose the level of security, but airline officials described the shutdown as ''sterile.'' That's when all passengers, regardless of destination or circumstance, are forced to leave the gated areas.

''We want to assure the public that their safety and security are our top priority,'' airport officials said in a press release. ''While we cannot publicly disclose current airport measures, we continue to employ multi-layered security system(s) to ensure the safety of all Hartsfield passengers and employees.''

A Delta pilot stood at one of the electronic billboards that displayed cancellation notices for every flight. Like thousands of others, he was lost for answers.

''To say I'm numb is an understatement,'' he said. ''How something like this can happen, I just don't know. What are we supposed to do?''

Airlines already were busy by early afternoon gathering pillows and blankets. The Georgia Emergency Management Agency worked through agencies around the state to find lodging for stranded passengers, estimated to number 30,000.

The FAA said the earliest any flight would be allowed to depart was noon today.