Private companies will be allowed to replace federal airport security screeners at U.S. airports by the end of 2005 under a plan announced yesterday by the Department of Homeland Security.

As many as 100 airports might be interested in the private workforce, airport groups and private screening firms said. Nearly all of the nation's 429 commercial airports are staffed by employees of the Transportation Security Administration, which was created after the terrorist attacks on Sept. 11, 2001. The law that created the TSA allows airports to apply this November to return to a private security workforce.

The TSA said that it will select the airports and qualified screening firms to perform the work and that it will maintain responsibility for oversight and regulation. Before the terrorist attacks, private firms conducted security screening through contracts with airlines.

Security companies said they could provide better screening services at a cost lower than the government's without lowering standards. A study conducted this year by consulting firm BearingPoint found that private security companies performing screening functions at five airports in a test program performed as well as federal screeners in detecting weapons. However, a Department of Transportation Inspector General report said both sets of screeners performed "equally poorly."

"Those of us in the service industry -- that's all we do, and it's not what the government does," said John DeMell, president of FirstLine Transportation Security, a firm that employs security screeners at Kansas City International Airport. "We hold all the experience."