Undated (AP) _ Airports were put on the highest level of alert and military bases around the nation quickly increased security after news of the U.S.-led attack on Iraq.

''People are busy as hell out there,'' said Federal Aviation Administration spokesman Dick Stafford, who announced in Washington that airports were on the ''highest level of security.''

The FAA has a four-stage security plan, with Level One representing normal operations. Level Four, the highest alert status, calls for the most intense precautions.

Stafford and another FAA spokesman in Washington, Fred Farrar, would not give details. But authorities at several airports said they were allowing only ticketed passengers past security points, suspending curbside baggage check- in, and warning that unattended vehicles will be towed instead of ticketed.

Stafford said no terrorist incidents were reported.

''Chances are the public would not notice any change at the airport,'' said John Case, chief of public safety at Blue Grass Airport in Lexington, Ky. ''We won't have machine-gun nests out front; we won't have armored personnel carriers like you'd see at Heathrow (Airport) in London. But people may see a police officer a little more often than they normally do.''

Authorities at several international airports said the Federal Aviation Administration ordered the increased security after the air strike was launched against Iraq. Security also has been tightened at the U.S.-Mexico border, power plants, dams, government buildings and military contractors.

Iraq has warned that a U.S. attack would unleash a wave of terrorism against American targets, although terrorism experts say an attack in the United States is unlikely.

Extra checking of identifications created backups of up to an hour for civilians trying to reach jobs at Davis-Monthan Air Force Base in Tucson, Ariz., home to A-10 fighter-bombers designed for anti-tank warfare, and Fort Huachuca, an Army post in Arizona specializing in communications.

A gate to Hunter Army Airfield in Savannah, Ga., closed 45 minutes earlier than usual Wednesday night. Military police stopped some cars and searched them.

''We have to be prepared against anyone who could be a terrorist,'' said an unidentified officer at the gate.

Access to the traditionally open Fort Benning near Columbus, Ga. was tightened slightly and a plan was formulated for closing access in case of threats, said Lt. Col. McDonald Plummer Jr., base spokesman.

Denver's Stapleton International Airport put new security measures into effect Wednesday night.

''We have closed concourses to all but ticketed passengers,'' said airport spokesman Richard Boulware. ''But all operations are running smoothly, and we are not even showing delays.''

The Port of Seattle police increased security checks of all entrances to the Seattle-Tacoma International Airport and stepped up their visibility in the terminal and on the road approaches to the airport, the port said.

Lambert Field in St. Louis added more police patrols to the terminals and police and bomb-sniffing dogs began to check luggage found unattended.

Wednesday night, Delta Air Lines quickly turned around two Germany-bound flights when war broke out in the Persian Gulf. Officials later learned the flights from Dallas and Atlanta could have proceeded.

Delta spokesman Bill Berry said the two flights bound for Frankfurt were directed to land at Hartsfield Atlanta International Airport because airlines officials were concerned about the security of the international flights.

''They were in the air at the time of the strike and we didn't want to take any chances,'' Berry said. ''The timing for them was just wrong.''

The two flights were later canceled.