Transportation Secretary Norman Y. Mineta followed a task force's recommendation on Friday and gave U.S. airlines 90 days to reinforce cockpit doors.

Mineta also said a $20 million grant program was created to fund other security measures, including the development and installation of transponders that can not be turned off. Transponders allow air traffic controllers to track planes.

Other security measures being developed under the grant program include video cameras and recording equipment to allow pilots to monitor the cabins of airplanes.

Several airlines had announced their intention to strengthen doors in the wake of the Sept. 11 attacks before Mineta's order came down.

American and United announced that they would install steel bars on cockpit doors; US Airways said it would strengthen the doors. Delta Airlines also has plans to reinforce the doors, according to the Transportation Department.

The task force had recommended either steel bars or other barriers be added to cockpit doors within 90 days. Mineta followed the recommendation and ordered work to begin in 30 days.

The changes will require the Federal Aviation Administration to approve both the devices installed and a method of installing them.

Until now, cockpit doors were designed to allow flight crews to quickly escape in case of an emergency. Steel bars on the doors or other measures to reinforce the doors and prevent terrorists from entering the cockpit would presumably have to allow for the same type of escape.

The task force made other recommendations that have not yet been adopted. Among them are the creation of a pre-screening process to allow passengers to get credentials that shorten the in-airport security screening and the creation of a new security agency within the Transportation Department to supervise that pre-screening.

In addition, the recommendations suggest limiting carry-on baggage to one bag plus a pocketbook or briefcase.

The Associated Press contributed to this report.