American and Northwest did not specify how many jobs would be affected by their reduction in service.

The cutbacks at Continental, the nation's fifth-largest airline, represent one-fifth of its work force of 56,000.

''These actions are a direct result of the current and anticipated adverse effects on the demand for air travel caused by this week's terrorist attacks on the United States and the operational and financial costs of dramatically increased security requirements,'' the Houston-based carrier said in a statement Saturday.

Continental Chairman and Chief Executive Gordon Bethune would not say when the employees might be called back to work.

Mr. Bethune said the airline has been losing $30 million a day since the attacks and only 55 percent of its planes are back in the air - most of them half-empty.

''We're taking immediate steps to preserve all the cash we had going into this debacle,'' he said. ''We are doing this in survival mode.''

Even before the World Trade Center and the Pentagon were hit by hijacked airliners, analysts predicted the industry would see huge losses because of the downturn in the economy.

But the figure has now ballooned to between $4 billion and $7 billion because of a drop in bookings caused by a fear of flying, the shutdown in air travel in the past few days, and the fewer flights and higher costs associated with the tight new airport security measures.

Without a huge bailout from the government, analysts say, bankruptcy is imminent for even the largest airlines.

''The airlines simply won't be able to do what they're being asked to do without financial support,'' said Helane Becker, an analyst at Buckingham Research in New York.

Congress gave President Bush $40 billion Saturday to help rebuild from the terrorist attacks. It was unclear how much of that might be allocated for the airline industry.

The Teamsters union is working with airlines officials to set up a meeting with Mr. Bush to pursue an emergency appropriations package for the airlines.

The nation's nine largest airlines have been losing between $100 million and $250 million daily since the nation's air space was shut down and then gradually reopened after Tuesday's disaster.

American, the nation's largest airline, became the first to announce scaled-back service when it did so Friday. United and Delta, respectively the second- and third-largest airlines, have not said whether they, too, will cut back. Northwest, the No. 4 airline, said it will complete a review by next week.

Also Saturday, Boston's Logan International Airport, where hijackers boarded the planes that destroyed the Trade Center, reopened to tightened security. Travel at other airports continued to creep back into service.

Reagan National Airport at Washington remained the only major U.S. airport still closed to travel. Federal authorities said its proximity to the Pentagon and other federal buildings make it a security risk.