Pan Am Corp., already weighed down by heavy debts and high fuel costs, said yesterday it will slash about 4,000 jobs because international travel is falling in the wake of the war in the Persian Gulf.

Pan Am, which has been operating under bankruptcy protection for almost a month, said nearly all of the cuts will be made at its main unit, Pan American World Airways Inc. With the gulf war dragging down passenger traffic and advance bookings, Pan Am already has cut its transatlantic schedule by more than 35 percent.

Pan Am said the 4,000 jobs will be eliminated through voluntary leaves, furloughs, attrition and transfers to United Airlines Inc. under a plan to sell Pan Am's prize London routes to United's parent, UAL Corp.

With the reduction of the 4,000 jobs, added to personnel cuts made last fall, Pan Am's employment level will fall 21 percent from the comparable period of 1990, it said.

The news came as Transportation Secretary Samuel Skinner told Congress he thought the number of big U.S. airlines would shrink to between three and seven in the coming year.

Now there are about a dozen big U.S. carriers, although two -- Pan Am and Continental Airlines -- are in bankruptcy court and a third -- Eastern Air Lines Inc. -- went out of business last month.

"We are moving toward the year of more than three and less than seven carriers we would be able to call giants," though several big regional airlines would remain, Skinner told a House subcommittee.

Richard Mathias, Pan Am senior vice president, told the subcommittee that American Airlines Inc., Delta Air Lines Inc. and United Airlines now are the only airlines with enough money to weather the current crisis of higher fuel prices and a drop in passengers because of the war.

The airline industry, deregulated in 1978, has been hard hit by energy prices stemming from the war and by fears of terrorist attacks that have cut passenger traffic.