FRENCH POSTCARDS -- AMC Carrollton, K-b bEthesda, K-B Studio, Roth's Manor.

You can hardly miss, with the joke about how the French worship American junk culture. Western movies dubbed in French, Le Drugstore on the Champs Elysees, Franglais -- it's so satisfying to administer a good ethnic slur to the French on the subject of taste, after all those decades of taking it from them.

But "French Postcards" manages to mess up the joke. Aside from a minute of "Star Trek" on French television, this sure-fire yuk doesn't work. This is particularly a shame because the film doesn't attempt to offer anything else, such as a story line of torrid sex.

The reason for the failure is that Gloria Katz and Willard Huyck, who wrote "American Graffiti" together, tried to jam all the old Franco-American jokes there are into one thin picture about American teenagers spending a school year in Paris. First they added the gimmick of translating literally what Americans who speak bad French say: "Yesterday we suffered the wet weather . . . Today, everybody is chestnuts." Bon.

But then they also added the joke about how Paris is obsessed with sex, and isn't that a surprise to people from Ohio? They have a young French girl who first insults an American stranger and then pulls him into bed. They have a French husband who neglects his beautiful wife for a mistress. They have a French older woman seducing a teen-age boy as education. They even have the routine about hiding unsuccessfully when the husband arrives home unexpectedly -- the joke that used to be known (in America) as French farce.

But these jokes, fine in their day, which was a long one, don't mix with the newer one about how French people are wild for American rock, American blue jeans, American sports cars and American food. Either Americans are naive hicks who are shocked when the French explains sex to them, or the Americans are leading the world in street culture with the French struggling to keep up.

To try both at once, you would have to be chestnuts.