The sound and light show at Mount Vernon, a Bicentennial gift to the nation from France, has proved to be something less than a box-office smash, and its season may be curtailed next year to reduce the deficit.

The Mount Vernon Ladies Association of the Union, which operates George Washington's home, will make a decision next month about what to do.

According to assistant curator John A. Castellani, attendance this season which runs from Memorial Day to Labor Day, was only 28,000. In Bicentennial 1976, when the show was inaugurated, attendance was 73,000. Castellani said the deficit this year will run between $10,000 and $20,000.

Castellani isn't certain why the show, unlike similar spectacles in France and elsewhere in Europe isn't popular, especially in a tourist mecca like Metropolitan Washington. In a sound and light show, colored lights play on historic sites as the history of the attraction is outlined.

"We've been told by some people that it's not something that attracts Americans," Castellani said. "It's a bit more intellectual than some attractions and it's a bit repetitive. You either like it or you don't."

There have been murmurings at Mount Vernon that the show's script, written in Paris, may dwell on France's assistance to the colonial revolutionaries at the expense of Washington and his domestic life. But this was emphatically denied by Castellani.

"That would be very unfair to the French," he said, adding, "but I'm a francophile."

At the French Embassy, first secretary Dominique Souchet expressed surprise that the show was having attendance problems, but said it was up to Mount Vernon to do what it wished. As to any grumbling about the show's script, he said, "Perhaps there are some Americans who don't know their history."

When the show opened, Washington Post critic Richard L. Coe wrote that it "might be subtitled, 'How the French Won the American Revolution.' . . . Why is Mount Vernon itself so neglected, treated as a mere way station, its cupola lighted while most of the time the soundtrack goes on about events in Williamsburg, Philadelphia, New York and Yorktown? . . . A great chance for sound and light been shortcircuited."

In an effort to increase attendance at the nightime show, which lasts 45 minutes and costs $1.50, Castellani said Mount Vernon will try to get some national promotional coverage for the spectacle. "It would make a splendid cover on Parade magazine, for example," he said.

Castellani said that some would-be visitors perhaps assumed that the show was held only during the Bicentennial. There are signs about the show on the road to Mount Vernon, but as Castellani said, a daytime visitor, especially if he is a tourist, might not have the time to return in the evening or find it inconvenient.

A survey taken among visitors showed that most of them were from the metropolitan area, even though Mount Vernon is a popular daytime tourist attraction. At night, however, both the mansion and grounds are closed, a possible factor in the lack of attendance.

To open those areas, Castellani said, would require additional expenditures for the extra personnel that would have to be on hand. The light show itself, he said, requires 12 to 15 people, ranging from technicians to ticket takers.