AMONG THE PROBLEMS we wish we had more often is what to do with leftover steamed crabs. Most of us conveniently avoid the problem by finishing them before they have the opportunity to become leftovers.

But sometime in August you just might have to face it head on.

First, keep them as fresh as possible before and after steaming. That means keeping the live crabs refrigerated (which also makes them easier to steam and helps keep the legs and claws intact) and discarding any that are not still alive when you cook them. Once they are cooked, it means picking out the meat the first chance you get. And keeping it cold. Don't try to freeze whole steamed crabs, since bacterial growth can occur in the interior before the crabs are frozen through. If you insist on freezing them, either pick them and freeze just the meat or only the meat-containing portions of the body and claws; plan on using them within three months.

Crabmeat becomes sticky and develops an ammonia odor and a yellowish color when it is spoiled; in any case, crab meat should not be kept in the refrigerator for longer than three to five days.

The next best thing to plain steamed crabs is a good crab cake. That means a lightly packed one, with just enough mustard and pepper to give it zest but not enough to interfere with the delicate sweet taste of the crab. And with the breading on the outside to hold the moistness in rather than on the inside to stretch the crab meat farther. A good crab cake is a light crab cake. And it needs nothing more to accompany it than lemon wedges and coleslaw.

To make the crab cakes you'll need a quarter of a pound of crab meat per person and a quick trip through the express lane of your supermarket plus salt, pepper, flour and oil or butter already in your pantry.

EXPRESS LANE LIST: Crab meat, eggs, mayonnaise, dry mustard, parsley, bread for crumbs, lemon, cabbage for coleslaw. MARYLAND CRAB CAKES (Makes 6 patties) 2 eggs 2 tablespoons mayonnaise 1 teaspoon dry mustard Salt and pepper to taste 1 pound picked crab meat 2 tablespoons finely chopped parsley Flour for coating Bread crumbs made from fresh bread for coating 4 tablespoons butter, oil or combination for frying Lemon wedges for garnish

Beat 1 egg lightly. Add mayonnaise, mustard, salt and plenty of pepper, whisking until smooth. Add crab meat and parsley and toss lightly but thoroughly. Shape into four cakes and carefully dip them in flour. Beat second egg in a shallow bowl and dip crab cakes carefully into egg, then into bread crumbs. Cover with waxed paper and refrigerate until well chilled and the coating adheres, at least 30 minutes. Heat butter, oil or a combination in a heavy skillet and fry crab cakes just until browned on each side. Serve garnished with lemon wedges and accompanied by coleslaw.