TONY RIVERS is a purist. Rather than cook with commercial chili powder that is, he says, "polluted" with cumin, oregano and black pepper, he makes his own.

Twice a year he sets three pounds of red jalapeno peppers ("they've got to be red") in a 250-degree oven for two to three hours, just long enough to turn them a deep brown, so they crumble to a powder at the slightest touch. Then he grinds them, sifts out the seeds and stores the powder in a jar away from the stove.

"The taste is a little less hot when they're red," he explains about his color preference, "but it is sweeter by comparison--sort of bell pepperish." On the other hand, commercial chili powders "give you a sweet black pepper taste," a flavor contrary to the taste he learned to love as part of his Caribbean Sephardic Jewish upbringing.

Plump, fresh red jalapenos are hard to come by in Washington markets, Rivers says. So four years ago, the freelance insurance broker and consultant bought his own jalapeno plant and raised it in an apartment window box. While the plant didn't produce all of the dozen or so green peppers his family of five eat in a week, it did produce all the "next to impossible to find" red jalapenos they wanted.

"It's a rugged plant," he says, "and will grow in anything as long as it gets plenty of sunshine." Unfortunately, when the family recently moved to a new condominium with no afternoon light, he had to leave his favorite living condiment behind.

Now he's back to combing the markets for perfect peppers and considers himself an expert at picking the premiums. The best selections can be found at roadside stands and the Latino strand along Columbia Road in Adams Morgan, he says.

"Next to serranos the only other peppers he keeps in the vegetable crisper , jalapenos are the hottest peppers," Rivers says. They're his family's favorite because, while they are hot, they are also full of flavor.

Peppers are best, he says, when they have reached the perfect balance of heat and flavor. Generally, jalapenos picked green and held until their skins turn blackish/purple "are the ones I live for." Look for dark green peppers with waxy coats (they will be waxy at room temperature, but when chilled their coats are dull, he notes). The stem should be firmly attached (overripe stems turn black and can be easily knocked off). If the pepper's skin is wrinkled it will still have heat, but no taste. Storing peppers loosely wrapped in plastic bags in the vegetable bin of your refrigerator will keep them fresh for two to three weeks.

Rivers' cooking includes the specialties passed down from his Moroccan and Curacao ancestors. Some of the dishes are delicate, others "will make you sit up and take profound notice" because of their spiciness, he says. These are a few of his favorites using jalapenos.

The red snapper with its classic hot pepper sauce is a great light dish, low in calories and high in fire. The salsa is but one of three standard mixtures he makes weekly to trade with friends for special recipes of their own and for everyday after-work munching. Be sure to use red jalapenos in the salsa for the characteristic sweet vegetable taste. Morrocan Meat Sauce is another hot tomato-based standard--slightly thickened, it excites any baked, broiled or steamed meat.

Wear rubber gloves and avoid touching your eyes when working with peppers, he warns, lest the volatile alkaloid, capsaicin, which accumulates along the inner walls of the pepper, leave its mark. TONY RIVERS' CHILI POWDER

Take two to three pounds of fat, ripe red peppers and lay them spread out near the oven to air-dry for two days. Put in the oven at 250-degrees and dry-roast slowly until the peppers turn a deep reddish brown (about 2 to 3 hours). Remove from oven and cool. Crush peppers, seeds and all, with a mortar and pestle. Strain through a tea strainer, to remove the largest seeds and store powder in a tightly covered jar. SALSA (Makes about 2 cups) 2 cups tomatoes, blanched, with skins and seeds removed 2 to 3 fat, thumb-sized red and green jalapenos, minced, with seeds left in 2 fat cloves garlic 1 small white onion, finely chopped Juice 1/2 lemon 1/2 teaspoon lemon rind

Blend tomatoes in blender until they form a coarse liquid. Mix in remaining ingredients. Let stand at least 1/2 hour or overnight before serving. MOROCCAN MEAT SAUCE (About 2 cups) 2 tablespoons butter 4 tablespoons flour 1 teaspoon salt Dash white pepper 2 cups beef or veal stock (if using canned beef broth, use half stock and half water) Slice ginger root size of a nickel 1 fresh jalapeno pepper, pierced 3 to 4 cloves garlic, pierced 10 crushed coriander seeds 1/2 teaspoon oregano (substitute 1/4 teaspoon oregano and 1/4 teaspoon savory) 1/4 teaspoon thyme 1/4 teaspoon ground cumin 1/2 cup tomatoes 1 tablespoon chili powder 2 to 4 tablespoons chili powder

Melt butter and cook until brown. Add flour, salt and white pepper and stir to a smooth paste. Add broth, bring to a boil and let boil for 2 minutes. Transfer to a double boiler to maintain even heat without scorching. Add remaining ingredients. Cook for 30 minutes. Strain and serve over any roast beef, steak or meatballs. RED SNAPPER HACHINANGO A LA VERACRUZANA (4 servings) 1 pound red snapper fillets 1 lemon 2 tablespoons light sesame or olive oil 1/2 cup finely chopped onion 2 to 4 garlic cloves, mashed 16-ounce can whole tomatoes, drained and coarsely chopped 3 tablespoons parsley, chopped 1 tablespoon vinegar 1 tablespoon red wine 1 teaspoon salt 1/2 teaspoon oregano (Mexican if possible) 1/4 teaspoon thyme 1 teaspoon sugar 1/4 cup water 10 large pitted green olives, blanched for 30 seconds in boiling water, sliced 2 green jalapeno peppers, chopped fine, with seeds removed Olive oil for sprinkling on fish

Rub fish with lemon. Fry 1 minute on each side in 2 tablespoons hot oil. Remove to a baking dish. Saute' onion, garlic and tomatoes in the oil left in the pan for 5 to 6 minutes. Add parsley, vinegar, wine, salt, oregano, thyme, sugar and water and continue cooking for 5 minutes. Top the fish with blanched olives and chopped peppers. Cover with the sauce and sprinkle with olive oil. Bake at 300 degrees about 30 minutes.