Kansas City, Mo. ? The nation’s transportation systems are safer now than before the Sept. 11 terrorist attacks, but the government will never be able to close every security gap, the head of the Transportation Security Administration said Tuesday.

“The bad guys are out there gaming everything we’re doing with respect to airports and any other mode of transportation,” James Loy told members of the National Defense Transportation Assn. “Our challenge has to be to find the means to try to stay ahead of them.”

Loy was in the city both to address the association’s annual meeting and to talk with security officials at Kansas City International Airport.

KCI is one of five commercial airports nationwide where employees of a private contractor — under TSA oversight — continue to screen passengers and baggage. The others are in San Francisco; Rochester, N.Y.; Tupelo, Miss.; and Jackson Hole, Wyo.

At the roughly 424 other commercial airports, about 50,000 federal employees replaced privately employed screeners last Nov. 19, as required by a new federal law. Those airports will be able to apply in November 2004 to return to private screening.

Loy already has visited KCI twice and, although not disclosing details, said the private screening operations seemed to be going “very, very well.”

The experience at KCI and the other four airports with private screeners will help guide decisions next year on whether to maintain the federal work force at all airports, he said in an interview.

“Our challenge is to make sure that when Nov. 19, 2004, rolls around, we have done a good job of making certain that airport directors can make a good, solid, objective decision about whether they want to reprivatize,” he said.

In his speech, Loy reviewed the TSA’s accomplishments since its creation by Congress shortly after the Sept. 11 hijackings, chiefly the strengthening of airline security through tougher screenings and the installation of thousands of explosive detection machines at airports.

Besides aviation — which Loy pointed out was Congress’ first concern — the TSA also oversees security of maritime, highway, rail, transit and pipeline transportation.

Loy said for all six methods of moving people and goods, the agency is devising security plans that involve awareness of threats, prevention and protection of terrorism, and response to terrorist acts.

Overall, Loy said, the goal is to “build a series of obstacles for the bad guys,” partly through the collection and sharing of information about people who use or work around various transportation systems.

The government plans eventually to issue Transportation Worker Identification Credential cards to truckers, longshoremen and others as proof of identity after background checks.

A separate initiative — the Computer Assisted Passenger Pre-Screening System, or CAPPS II — is aimed at making air travel safer and more efficient.

For CAPPS, commercial and government databases will be used to rate passengers as possible security risks who merit extra screening. Unless a passenger is flagged as a terrorism risk, the information will be discarded after a flight, Loy said.