AT LAST! Washington has joined other big cities around the country and will have its very own farmer's market. It's taken more than two years to get the idea off the ground, the cooperation of the city, federal government and private individuals and the determination of a man called Al Smith. Smith is with the University of D.C. Eextension Service. But he has had a lot of help from the mayor's office, particularly Mildred Brooks, who has been fighting for a farmer's market for a couple of years.

On June 24 the market will open at Kennedy Stadium. Farmers from as far away as New Jersey will be there with fresh fruits and vegetables Tuesday and Thursday afternoons each week during the growing season.

At the moment many of the agencies involved, including the Armory Board and the National Park service, are donating their services and the space. But if the market is successful, fees will be charged.

Smith said the market is an experiment. If it works, which means if D.C. residents support it, smaller markets will be set up in neighborhoods so that people without transportation can enjoy the low prices and high quality of the farmer's produce.

Jackie Onassis would be proud. Her White House Chef, Rene Verdon, has wrested the Toque d'Argent away from New York.

The prestigious award, sponsored by the Maitres Cuisineres de France, a group of about 400 French chefs working in the United States is awarded to one of its members each year.

Verdon, who is chef-owner of the elegant Le Trianon in San Francisco, received the award in New York a few weeks ago.

Verdon stayed on at the White House for a short time during the Johnson Administration. But when the Housekeeper told him he had to cook from recipe books, he handed in his white toque with his notice.

On a sadder note, the creative Frenchman who gave Los Angeles its best taste of fine French cuisine died earlier this month of a brain tumor. Jean Bertranou, chef and one of the owners of l'Ermitage, which changed the face of that city's dining, had been ill since the fall. He was buried in the small town in France from which he came.

Michel Blanchef, who has been cooking in Bertreneau's place since he became ill, will take over a chef.

From haute cuisine to fast food. . . Tater Junction has set up shop on 14th Street, near K. Carry-out or eat-in, the only main course the chain serves is a baked Idaho potato with your choice of 18 toppings, which change from day to day.

In addition to a notation on the menu that potatoes are 99.99934 percent fat-free and are not fattening, there is a description of the possible toppings, not all, but most of which are fattening. . . and quite good.

Of course, you don't have to have anything on top of the potato, but the kind of will power is not in great supply. You can choose from Po'Boy Stroganoff, Chill Mexicana, Polynesian Meatballs and other less exotic toppings such as mushrooms sour cream, butter and cheese. a

Tater Junctions have already made their mark in 16 other cities and as soon as the cashier can figure out how to work the cash register, the line should move swiftly.