The nation's major airlines have finished installing bars and other equipment to strengthen cockpit doors, industry officials announced Thursday.

The stronger doors are designed to prevent hijackers from getting into the cockpits, as was done Sept. 11.

The Air Transport Association, the trade group for airlines carrying 97 percent of all passengers, said the carriers completed strengthening the cockpit doors within a month of the attacks. A Transportation Department task force recommended the step to improve security.

"This is so crucial as we go into the holiday season," said Carol Hallett, president of the airlines' trade group. "Americans across the board can have full confidence."

The steps to strengthen the cockpit doors are only an interim move. The Federal Aviation Administration, the airlines and airplane manufacturers are designing new, stronger doors to be installed on all airplanes. The doors will be designed to both stop a bullet and to prevent someone from kicking them in to gain entry to the cockpit.

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

Traditionally, cockpit doors have been designed to let pilots easily escape in the event of an emergency. But the Sept. 11 attacks, when terrorists took over four commercial jets and crashed two of them into the World Trade Center and a third into the Pentagon, forced airline officials to instead come up with ways to keep intruders out.

David Stempler, president of the Air Travelers Association, said the improvements would be welcomed by passengers.

"Passengers should feel more secure because we have the pilots protected behind a locked cockpit door," Stempler said. "This way, planes can't be turned into cruise missiles."