Two ground crew employees cleared the checkpoint with a pocketknife and a corkscrew while a pilot passed without proper identification, airport spokeswoman Suzanne Luber said.

''Once they did that, they turned around and said, 'Hey, look what we did,''' she said. Their point: to show that security gaps still exist days after terrorist attacks in New York and Washington, she said.

Airport officials evacuated the terminal's north concourse and swept it for dangerous materials. Nothing was found and the concourse was reopened.

Luber said she did not know what happened to the three employees. ''We would ask that nobody intentionally try to break security,'' she said.

Federal Aviation Administration spokeswoman Madelyn Sawyer said it was investigating the actions of the airline employees and of the security workers.

Northwest spokeswoman Mary Beth Shubert said: ''We are concerned about these reports, and we plan to cooperate thoroughly with the airport authorities and take appropriate action.''

Northwest provided limited service for a short time Thursday but canceled all flights by evening.

Schubert said earlier in the day, ''external information has come to our attention which indicated that it is not prudent to operate this evening.'' No other details were released.