Urging Americans to fly on commercial aircraft, President Bush on Thursday announced plans to deploy National Guard troops to temporarily protect U.S. airports while broad security measures are implemented.

"Get on the airlines, get about the business of America," Bush told thousands of airline workers at Chicago's O'Hare airport. "Everybody here who showed up for work at this important industry is making a clear statement, that terrorism will not stand."

The president's plans to provide $500 million to strengthen airplane cockpit doors and implement federal oversight of airport inspections are intended to help restore security and confidence in the U.S. airline industry, which was crippled by the hijacking attacks on New York and Washington.

Bush said Wednesday he was offering the "confidence-boosting measures and some concrete proposals" to "convince the American public it is safe to fly."

"One of my concerns is that this terrible incident has convinced many Americans to stay at home," he said. "And one of the keys to economic recovery is going to be the vitality of the airline industry."

Bush's plan includes:

—Expanding the use of federal air marshals aboard commercial airliners. "The requirements and qualifications of federal air marshals are among the most stringent of any U.S. federal law enforcement agency," the White House statement said.

—Spend $500 million on plane modifications, including efforts to restrict the opening of cockpit doors during flights, fortify cockpit doors to deny access from the cabin, alert the cockpit crew to activity in the cabin and ensure continuous operation of the aircraft transponder in the event of an emergency. The transponder allows air controllers to track a plane.

—Put the federal government in charge of airport security and screening, including the purchase and maintenance of all equipment. The government would supervise passenger and baggage security and perform background checks on security personnel.

"Fully implementing the extensive security proposal may take four to six months," the White House statement said. "During that time, the president will help ensure that every airport has a strong security presence by asking the governors of the 50 states to call up the National Guard — at the federal government's expense — to augment existing security staff at every commercial airport nationwide."

Other considerations include the installation of cameras to monitor jetliner cabins, White House officials said.

Bush's plan does not include arming pilots, action requested by the pilots themselves. "There may be better ways to do it than that, but I'm open for any suggestion," Bush said Wednesday, as aides privately confirmed that he is cool to the idea.

Bush's trip to Chicago was the second time he has traveled on Air Force One since the Sept. 11 airplane attacks on New York and Washington that left nearly 7,000 dead or missing.

Transportation Secretary Norman Mineta boarded a commercial flight Thursday at Baltimore-Washington International Airport to demonstrate his confidence in the air system. He was bound for Chicago to join Bush, accompanied by Jane Garvey, head of the Federal Aviation Administration.

Mineta waited in a long line at a BWI security checkpoint. He placed a leather bag on a scanner's conveyor belt, took out his keys and walked through the metal detector. It beeped, prompting a security guard to give Mineta a thorough sweep with a hand-held detector before allowing him onto Concourse A.

Bush's father, the nation's 41st president, planned a news conference at Logan Airport in Boston to reassure Americans before flying from Boston to Houston.

The White House is also eager to convince the public that life is returning to normal, and getting Americans back onto airplanes is part of the effort.

White House spokesman Ari Fleischer said the number of commercial flights each day had returned to near normal, now at about 5,500, compared with the maximum before the attacks of 6,500.

However, relatively few people are on those flights. Delta Air Lines, for example, said its planes typically are only 35 percent filled.

The Associated Press contributed to this report.