President Bush will announce an expanded role for National Guard troops at airports, including putting them at boarding gates, administration officials said Thursday.

Bush planned to make the announcement Friday at a White House ceremony honoring private-sector employers of National Guard and Reserve personnel, the officials said, speaking on condition of anonymity.

One official called it a "dramatic increase" but wouldn't provide details.

Under existing arrangements, governors of the states have stationed Guard personnel in some circumstances at security checkpoints, where passengers and carry-on baggage are screened. Also, guardsmen have been used for general airport patrol duty.

Bush's initiative would give airports and airlines an additional measure of security by having guardsmen witness passengers who have been checked through security and are in the process of boarding aircraft.

Meanwhile, with the approach of the holiday season, the nation's major airlines announced Thursday that they have finished installing bars and other equipment to strengthen cockpit doors.

The stronger doors are designed to prevent hijackers from getting into cockpits, as they did Sept. 11.

Transportation Secretary Norman Y. Mineta ordered airlines in early October to strengthen the doors. The Federal Aviation Administration then issued rules allowing airlines to do so without following normal requirements for modifying planes.

The airlines completed the work within a month, installing steel bars and latches on the cockpit side of the door. The bar is pushed into place by the pilot, preventing anyone in the airplane cabin from entering the cockpit.

"This is so crucial as we go into the holiday season," said Carol Hallett, president of Air Transport Association, which represents the major airlines that carry 97 percent of passengers. "Americans across the board can have full confidence."

Even so, the annual AAA survey for Thanksgiving travel forecast 4.6 million people traveling by air, a 27 percent decline from last year's 6.3 million. That translates to 13 percent of the 34.6 million people expected to travel 50 miles or more from home this Thanksgiving, down from 17 percent in 2000. On other hand, 87 percent will travel by car, the highest percentage ever recorded by AAA and up from 83 percent last year.

Cockpit doors on airplanes have been designed to allow flight crews to escape quickly in an emergency. But after the terrorist attacks, airline officials instead turned their attention to keeping intruders out.

FAA spokeswoman Alison Duquette said increased security took precedence over allowing pilots an easy escape.

"There's a security threat today that did not exist when airplanes were first designed," Duquette said.

The steps to strengthen the cockpit doors are only an interim move. The FAA, the airlines and airplane manufacturers are designing new, stronger doors to be installed on all airplanes. The doors are to be designed to stop a bullet and prevent someone from entering the cockpit, while still allowing pilots to escape.

Ken Hylander, vice president of safety and engineering for Northwest Airlines, said he hoped those new door standards would be finished within a month.

Other safety measures have also been put in place. Transportation Department and FAA officials acknowledged that pilots flying into Reagan National Airport must recite a password before air traffic controllers can clear them to land.

Unless they hear the password, which is changed daily, controllers divert the planes to Dulles International Airport. This happened three times in the past month.

"When controllers hear the password, the plane is cleared to land at Reagan. Otherwise, it's diverted to Dulles," Mineta told the San Francisco Chronicle editorial board.

Flights in and out of National have been operating at a higher level of security than flights elsewhere because of the airport's proximity to the Pentagon, White House and other government buildings. For example, passengers cannot leave their seats during the last 30 minutes of a flight into National.