The D.C. Open Air Farmers Market is still going strong at RFK Stadium. Or to be more precise at the stadium parking lot at the corner of Oklahoma Avenue and Benning Road.

So strong, as a matter of fact, its schedule has been extended by a month, until Nov. 25. Since it opened in June it has attracted 2 to 3,000 customers each Tuesday and Thursday and on some days almost twice that number.

The buys are as good as ever, the vegetables and fruits, literally farm fresh, coming as they do from Maryland, Virginia and other nearby states instead of from across the country.

Last week, while tomatoes were selling in the supermarket for 89 cents a pound, the market had them for 50 cents; zucchini was 40 cents a pound and 69 cents a pound at the grocery store; butternut squash was 24 cents a pound cheaper at the market; acorn squash, 34 cents a pound less. One dollar would buy you four peppers at the supermarket and five at the outdoor market.

A fish farmer was selling a pound of backfin crab meat for $5.90; 2 1/2 dozen extra large eggs cost $2.25.

The market, a joint venture of the D.C. Cooperative Extension Service, the Mayor's Commission on Food and Nutrition and Health and local farmers has had better than usual cooperation from other branches of the District government and the U.S. Department of Agriculture. Al Smith, who has been largely responsible for the market's success, says there are solid plans to open a smaller market in Anacostia next year and some hopes of opening markets in other inner-city neighborhoods. There is even talk of opening one at Metro Center.

Market hours until Nov. 25 are from 1 p.m. until dusk.