President Bush has signed into law a bill that tries to close gaps in airline security turned up by the families and friends of those killed in the bombing of Pan Am Flight 103 over Lockerbie, Scotland, in December 1988.

"The relatives and friends of the Pan Am victims deserve great credit for their persistence in helping to improve aviation security," Bush said in a printed statement Friday.

The legislation grew out of recommendations made by a presidential commission on aviation security and terrorism that Bush set up last year.

The new law strengthens the role of the federal government in airline security by requiring the appointment of federal aviation security managers at all major airports where security programs are handled by private contractors.

It also upgrades training standards for security workers and shifts responsiblity for security policy-making to the Transportation Department from the Federal Aviation Administration, which is one of the department's bureaucratic components.

In deference to the friends and relatives of the Pan Am Flight 103 victims, the legislation directs the State Department to improve its procedures for dealing with the families of terrorism victims.

It also asks the department to develop guidelines on when to warn the public of serious threats to airline security.