The dollar is in trouble on foreign exchanges, and the balance of payments is unbalanced. But one U.S. export is doing better than ever: the all-American model.

In fact, when the marathon showings of French ready-to-wear begin in Paris next month, as many as one out of every three models coming down the runways will be an American.

Many of them have moved to Paris to supply the demand. Others slip in with tourist passports, pay sizable percentages to French modeling agencies, and still slip back home with acceptable cash wages, thicker portfolios of photos, and very pleasant memories.

One such model who has made a new start in the Old World is Washington-born Gloria Burgess. She now lives in Paris, works the shows there and in Milan, and does as many as 30 a season -- at the rate of about 2,000 francs ( $500) per show.

Actually Burgess says she would make better money in New York, since there she would be paid by the hour rather than by the show. But she doesn't enjoy living there and besides, "clothes in Paris are far more fun to wear," she says. "In New York even the 'way-out' designs are far more conservative than in Paris."

The total number of models working the Paris shows -- and at the Porte de Versailles, where hundreds of manufacturers from all over the world exhibit their wares -- is in the thousands. But during the week or so of the Paris ready-to-wear presentation, designers tap a select pool of about 75 models, at least 20 to 30 of whom are Americans: some living in Paris, others arriving just for the showings in Paris and Milan.

Those huge, often extravagant fashion shows with vast international audiences and hundreds of photographers are ideal showcases for American models. But more important for those just getting started are the tearsheets they can compile from photo sessions for magazines in Europe. Models who work the shows may also be photographed in the most avant-garde clothes by unusually inventive photographers; and even the paper used in the European fashion magazines is often a higher quality than in some American publications.

Pierre Cardin checked out dozens of male models for his recent menswear show in Paris and in reviewing nationalities afterward was very surprised: Each one he had chosen was an American. "I didn't expect it," he said. "But the look and the proportion was exactly right."

He uses a number of American female models, too. "They move quickly. They are professional. You don't have to wait for them," says Cardin. "If [French] models are slow, you must wait. If you say something to hurry them up, it shows in their faces. But with Americans, they are always ready on time."

"French girls are not disciplined, American girls are," says designer Karl Lagerfeld. "Swedish girls -- I never liked their looks. Yves Saint Laurent likes the exotics. Me? I like Americans. I like their broad shoulders, their proportions." Ramona Ridge, who once lived in Washington, and graduated from Madison High School in Vienna, Va., is a Lagerfeld favorite.

Model Marion Womble thinks the close relationship between designer, photographer and model is an advantage of working in Paris and Milan, too. "In New York, people are not as casual. In New York you do a show and that's it. In Europe, the people you work with become your friends." Although he averages $750 a working day in New York, $450 is typical in Paris -- but it's still worth it. "Just think of the trips. I was just in Japan with Kenzo," he says.

For highly successful model Donna Palmer, the reward -- as much as the money -- is the excitement of being fitted by designers such as Yves Saint Laurent and doing the shows, as well as a round of parties and dinners and a lot of shopping in Paris and Milan.

Marcie Hunt, who now lives in Paris and has four covers of English Vogue to her credit, has another reason for staying: her French boyfriend.

"Americans are not 'pretty pretty'," says model agency head Karen Mossberg, a former model herself. "But they are personal, outgoing, healthy. They are sportive looking and work very hard. And they are tall and have good skin so the photographers like them," she says.

In addition to the wide exposure of the shows, says Mossberg, is that "the photographers here give them more freedom for pictures. They are often running, moving. And if they are inexperienced, they can learn a lot from people who have worked here a long time."

Mossberg says that her agency advances money to the models before she is reimbursed by the magazine or designer. Besides commission, she says, the agency takes out taxes. French authorities have "looked through their fingers" about proper working papers. "It's okay as long as their taxes are paid," she insists.

American models are popular in Milan, too. And two years ago, the back stage of at least one designer showing was visited by police checking for "illegal" models, a few of them hid in an upstairs hotel bedroom until the police left. On another occasion, police demanded that certain unregistered models leave the show or it would be stopped.

Now, most American models working in Italy register with the questuna (police) as well as with the labor ministry, and they have no problems working for a short period.

"In France there is a new law coming," says Francois Lano. owner of Paris Planning, a Paris modeling agency with a New York office. Meanwhile, he says, you can have a permit to work if you apply before leaving the United States.

But at least one top Paris designer flies a pet American model or two over for shows -- paying airfair and salary and skipping all of the "formalities" of proper working papers.

Guy Bishop said one French agency told him not to get working papers but to come to Paris as a tourist. He arrived for the last round of showings in Paris with $20 in his pocket. His plane ticket and lodging were provided for him by the agency, which also arranged a wake-up call daily and offered to do his laundry. "If I don't get work, they don't get any money either," says Bishop.

He has been paid as much as 3,900 francs ( $990) for a single assignment -- but after the agency took their share, he got about 2,000 francs. "You never see the difference because it all goes directly to the agency," says Bishop. "You might as well just throw it away."

Men are generally paid less than women, says Bishop, but "they have hair and make-up to worry about, and besides there is a lot more competition for those jobs."

Says Bishop philosophically, "You know you are being exploited in Paris, but you can't do anything about it. I have to think of it as a paid vacation. There isn't any place I can complain if I wanted to."

One place that is not hearing any complaints is the Labor Ministry in Paris. Officially, says the French consulate in Washington, if you want to work in France you need two things -- a carte de traveil (working permit) and a specific job offer. To get the carte you must apply to the consulate and have them direct your file to Paris, where the authorization is issued.

Before the 1970s you could slip by without a permit, admits a French Embassy official, "but that has all changed now." For the last four years, a serious effort has been made to curb immigration because of increasing unemployment (1.4 million people in France today -- 5 percent of the population).

"Now we pay people to go back to their countries."

But no one is paying American models to go home. If they did, the price would have to be very high.