NEW YORK (AP) _ American businesses operating in Panama scrambled today to assess the impact of the U.S. military invasion, closing some offices and checking whether the fighting endangered their employees.

The government estimates 35,000 Americans live in Panama, many of whom work for U.S. corporations.

Texaco Inc. said only that all the company's employees are safe. ''That's all we're prepared to say ... it's just too preliminary to make any other comment,'' he said.

Texaco owns a large refinery in the Colon area, near the Panama Canal. The refinery has a capacity to handle 100,000 barrels of crude each day.

Citicorp closed the six branches it operates in Panama City today. ''We're still trying to find out whether anybody's affected,'' said spokesman Ken Campbell.

Merrrill Lynch & Co., one of a number of firms to leave Panama following U.S. sanctions against the country announced in 1988, moved its operations to the Cayman Islands last year.

The Panama Canal, where about 30 ships cross the isthmus daily, was closed at 1 a.m. because of the fighting, according to Panama Canal Commission spokesman Franklin Castrellon.

Shipping analysts would not speculate on how long the canal could be closed and noted that alternate routes and other forms of transportation could help diminish the impact if the canal were closed for an extended period of time.

''The amount of traffic going through the canal is probably not going to cause the economy to collapse,'' said Mark Degenhart, an analyst with Argus Research Inc.

''Goods shipped in containers can be transshipped by railroads'' from the west coast to their east coast destinations, he said.

Companies with ships en route to the canal are proceeding as usual in hopes that the canal will be opened by the time their ships arrive.