IF ETERNITY IS two people and a ham, what is two people and a seven-pound rockfish?

I had invited some friends over for sushi. Normally, it's not a good idea to specify a menu in advance, unless you're planning to serve spaghetti with meat sauce or refried beans. You don't know what you'll find in the stores. But we had been talking about the difficulty of finding good sushi in Washington, and I had boldly offered to try to do better than the local restaurants. I set off for the Maine Avenue fish market.

I have not yet found fresh tuna at any of the fishmongers in the city (although some have told me they do get it occasionally). Mikado's food store had some a few days before New Year's, but it looked a bit dried out around the edges -- especially unacceptable at $18 a pound. Perhaps sushi without tuna is sacrilege, but sushi with fish that is not perfectly fresh is blasphemy.

I was lucky. Custis and Brown, one of the Maine Avenue dealers, had some of the freshest rockfish I'd seen in a while. I was told that the fish -- better known to Japanese cooks as striped bass -- had just come in an hour before and had been caught that morning. "They were swimming last night, ma'am." They had the bright, clear eyes and the firm flesh to prove it.

The smallest one was nine pounds. My sushi was to include pickled mackerel, shrimp, squid, perhaps octopus, fish omelet and cucumber -- I would need no more than half a pound of rockfish for six people. But the fish winked at me knowingly, and I bought it.

The sushi was wonderful. I believe the flesh from a large bass is richer and tastier than the flesh from a small one.

After the dishes were clean and the wasabi paste was back in the cupboard, there were two pounds of filleted fish in the refrigerator, and another couple of pounds of head and carcass. The sushi had been so good that we would be happy to eat it again the next night -- just two of us, though, and being extravagant would take care of only another 6 ounces or so.

I am normally very hesitant to freeze fish, but I was not prepared to have another dinner party the following night. I trimmed the thin belly flap off the remaining whole fillet and set it aside. Then I cut the fillet in half crosswise -- the skin still on -- and froze the two pieces, carefully wrapped. Each piece weighed about 10 ounces.

The two flaps of flesh that cover the belly of the fish are fattier than the other meat, and I thought they would do well in a fish stew. I cut them into 2-inch squares, along with other small scraps of fish that had been trimmed from the fillets. The tentacles and fins of the squid from the sushi were left over as well. I made a light garlic, tomato and wine sauce, cooked the fish in it ever so briefly, and put the whole stew in the refrigerator in its stainless steel pan. With a small loaf of Italian bread and a salad, the meal for two was different enough from sushi that we didn't mind eating rockfish a third night in a row.

The head and carcass went into one of my favorite dishes: pasta with fish-head sauce (after a recipe from Marcella Hazen's "More Classic Italian Cooking"). It's the kind of food -- like French cabbage soup or coarse-grained bread -- that fulfills all my fantasies of being a peasant woman. Call me Marie Antoinette -- for these dishes are as rich in flavor as they are humble in origin. Fish-head sauce is similar in many ways to the fish stew I had made, but I make the pasta sauce spicy with hot red peppers, which changes its character.

There was enough of the sauce from my big bass to serve four, and I invited some friends over to share it later in the week. I did not announce to them in advance that I planned to serve "fish-head" sauce. Guests will not know what part of the fish the delicate meat came from until you explain. If they're squeamish, let them taste it first.

I didn't approach the fillets in the freezer until the following week. The first one was brought out when my brother came to visit and wanted Chinese food for dinner. I steamed the fish with black bean sauce. Although that preparation is classically used on a whole fish, it worked well with the fillet, which stayed nice and moist despite having been frozen.

The last fillet ended up in a quick white wine sauce after work a few days later. Defrosted in the refrigerator overnight, marinated briefly in white wine and olive oil, and poached in the oven for about 15 minutes, the fish was again juicy and tender. I don't know that I would try broiling fish that had been frozen, but after two weeks in the freezer, the fish was quite delicious cooked by moist heat.

The primary lesson from this continuing fish menu was that when the craving for sushi hits, one need not be intimidated by the size of a good, fresh rockfish. With a little organization, you can have six excellent meals for the price of one at a sushi bar. SUSHI (6 servings)

I made chirashi sushi, which is not on the menu at most local restaurants but can usually be ordered anyway. Chirashi is a bowl of vinegared rice with an assortment of fish and other delicacies laid over the top. It's usually a good value in a restaurant and, if you are not a skilled sushi chef, a much more manageable way of serving sushi at home than nigiri sushi, the little ovals of rice surmounted by slices of fish. 8 ounces very fresh rockfish fillet 2 small squid 12 medium shrimp, in their shells 1 teaspoon sugar 1/2 teaspoon salt 2 tablespoons rice-wine vinegar or white vinegar Pickled mackerel (recipe below) Fish omelet (recipe below) 1/2 cucumber Pickled ginger Wasabi paste Sushi rice (recipe below) 1 sheet nori (Japanese pressed seaweed) Soy sauce

Slice the rockfish across the fillet into slices 1/8-inch thick.

It is very difficult to find squid that has not been frozen. Fresh squid can be cleaned and sliced into neat parallelograms; if the squid has been frozen, I parboil it by dropping the sacs into boiling water and taking them out as soon as the water returns to a boil. Reserve the tentacles and the fins for another use (see the fish stew below).

Insert a toothpick along the underside of each shrimp to straighten out the body. Parboil the shrimp in the same way as the squid. Remove the toothpicks, shell the shrimp, devein them, and slice almost all the way through from bottom to top, so that the shrimp can be opened flat. Press the shrimp gently with the side of a cleaver to flatten them. Dissolve the sugar and salt in the vinegar; place the shrimp in a small bowl and toss in the vinegar dressing.

Cut about 24 neat slices of the mackeral fillets.

Cut 12 slices of fish omelet, about 3/4-inch-by-2-inches and 3/8-inch thick.

You should have one lengthwise half of a cucumber or two lengthwise quarters. Seed the cucumber and sprinkle it lightly with salt; let it rest about 20 minutes. Wrap it in a paper towel and press down on it to extract some of the water and soften the flesh a bit. Slice it thin.

Slice the ginger as thin as possible. Reconstitute the powered wasabi by adding just enough water to about 1 tablespoon of the powder to make a thick paste.

Portion the rise among six wide bowls, and spread it into a neat layer in each.

Toast the nori slightly by passing it over a heated stove burner several times. Cut it into slivers with scissors and sprinkle it over the rice in each bowl.

To eat the sushi, each person transfers the wasabi paste to a small side dish and dissolves as much of it as he wants in a small amount of soy sauce. The fish is then dipped in the soy sauce mixture one bite at a time, and eaten with the rice. PICKLED MACKEREL 1 mackerel Salt Rice-wine vinegar or white vinegar

Start three days before you want to serve the mackerel. Fillet mackerel as carefully as possible, but don't worry about leaving a few small bones; they will dissolve in the pickling process. Heavily salt the fillets; place them in a nonmetallic dish just big enough to hold them in one layer (the fillets may be cut in pieces if necessary); cover and refrigerate overnight.

The next day, pour off any liquid that has accumulated. Add vinegar just to cover the fish.

The next day remove the fish from the vinegar. It should be a dull, opaque gray. Pull away the skin, which should come away in a thin membrane, leaving a very shiny silvery blue coating on the mackeral. FISH OMELET 1 ounce fish fillet (flounder or sole is ideal, but I used, as you may guess, a bit of rockfish) 3 eggs 2 teaspoons sugar 1/4 teaspoon salt Vegetable oil

Preheat the oven to 300 degrees. Puree the fish in a food processor or blender until perfectly smooth. Mix in thoroughly the eggs and seasonings.

Coat the bottom of a small, overn-proof frying pan with a thin layer of oil. Warm over medium heat, and pour in the egg mixture. When it just begins to set on the bottom, move the pan to the oven and bake about 1/2 hour, until firm. Turn out the omelet and let it cool. SUSHI RICE 2 cups short-grained white rice 1/3 cup rice-wine vinegar or 1/4 cup white vinegar 2 tablespoons sugar 1 tablespoon salt

Place the rice in a wide, 2- or 2 1/2-quart pot, and rinse it in several changes of water to wash away surface starch. (Although this procedure washes away some of the nutrients added to fortified rice, I think it's necessary in making rice for sushi.) Add 2 cups cold water; cover the pot and bring to a boil over high heat. Immediately lower the heat to a low simmer, and cook the rice for 10 minutes. Turn off the heat, but leave the pot on the burner, without removing the cover, for another 10 minutes.

While the rice is cooking, heat the vinegar and seasonings in a small pot until the sugar and salt dissolve. Set aside.

After the rice has sat for 10 minutes, turn it out onto a wide platter -- a jelly roll pan will work fine. Pour the vinegar over the hot rice, tossing the rice at the same time with a rice paddle or a wooden spoon. Get someone to help you by fanning the rice while you are tossing it, or train a table fan on the rice: the idea is to cool the rice as quickly as possible. A SMALL FISH STEW (2 servings) 2 teaspoons olive oil 1 small onion, chopped 1 large clove garlic, finely chopped or mashed 8 ounces (approximately) boneless fish (I used pieces of the rockfish and the tentacles and fins of the squid from the sushi, cut into small bite-size pieces) 1/3 cup dry white wine or dry vermouth 1 cup homemade tomato sauce Salt Pepper 1 tablespoon chopped fresh parsley

Place the oil in a medium-size stainless steel or enameled frying pan; cast iron or aluminum will react with the wine and tomatoes. Saute the onion and the garlic in the oil until translucent. Add the fish pieces and toss until they just turn opaque. Add the wine, bring to a boil, and let it bubble away for a minute. Add the tomato sauce and salt and pepper to taste. Simmer just until the fish is cooked through -- about 5 minutes. Serve right away or let it cool and reheat it, as briefly as possible, later. Just before serving, stir in parsley. FISH-HEAD SAUCE (For 1 pound of dry paste) Head and carcass of a large rockfish (you will need about 2 pounds, but a few heads from smaller fish, and other kinds of fish, will do just as well) 3 tablespoons olive oil 1 medium-sized onion, chopped 2 large cloves garlic, finely chopped or mashed 2 dried red hot peppers 1/2 cup dry white wine or dry vermouth 2 cups canned plum tomatoes, with their juice Salt Pepper 2 tablespoons chopped fresh parsley Cut the carcass of the fish into pieces that will fit in 1 layer in a wide stockpot; set aside. Place the olive oil in the pot, add the onions and garlic, and saute over a low heat until just translucent. While the onions are cooking, seed the hot peppers, chop them finely and add them to the pot.

Push the onions to the side of the pot, raise the heat to medium and add the fish pieces. Browm them very lightly on all sides. Add the wine; let it bubble away for a minute or two. Add the tomatoes and their juice; bring to a boil and let simmer for about 20 minutes.

Remove the head and bones from the sauce; continue to simmer the sauce until it is reduced by about one quarter; add salt and pepper to taste.

When the bones are cool enough to handle, carefully remove all the meat from them and from the nooks and crannies of the head.

You can store the sauce and the fish separately in the refrigerator for a few days. When you are ready to serve, bring the sauce to a simmer, then return the fish to the sauce and just heat through; cooking too long at the point will dry out the fish. Stir in parsley.

Serve over pasta; I prefer this robust sauce over pasta secco -- spaghettini, linguine, penne -- rather than fresh pasta, because I think the textures go better. Grated cheese does not go well with this sauce. STEAMED BASS WITH CHINESE BLACK BEAN SAUCE (2 servings) 1/2 tablespoon Chinese sesame oil 10-ounce fillet of striped bass (rockfish) 1 tablespoon preserved black beans (available in Oriental groceries) 1 medium clove garlic, finely chopped or mashed 1 large scallion 1 tablespoon slivered fresh ginger

Coat a small platter lightly with sesame oil. Place the fillet on the platter, skin side up. Score the skin with 3 or 4 shallow parallel cuts.

Press the black beans with the side of a cleaver to crush. Heat the remaining sesame oil in a small frying pan; saute the beans and garlic a bit to release their flavors. Spread this mixture over the fish.

Slice the scallion on a diagonal into 1/2-inch pieces. Sprinkle the scallion and the ginger over the fish.

Place the platter in a steamer -- I use a very large frying pan -- and set the platter on a muffin ring to king it above an inch or so of water in the bottom of the pan -- and steam for about 15 minutes. FISH WITH WHITE WINE SAUCE (2 servings) 1 tablespoon olive oil 1/3 cup dry white wine or dry vermouth 1 scallion, minced White pepper 10-ounce fillet of rockfish 1 tablespoon butter 1 tablespoon butter 1 tablespoon flour 1/2 cup cream Fresh lemon juice Salt Fresh parsley, chopped

Mix the olive oil, wine, scallion and a big pinch of white pepper in a non-metallic baking dish just large enough to hold the fillet. Add the fillet and turn to coat it with marinade. Let the fillet marinate for about half an hour or an hour. Bake, covered, at 400 degrees until just done -- about 10 to 15 minutes. Remove the fish from the liquid and place it on a small platter.

Melt the butter in a small frying pan. Add the flour, stirring rapidly until smooth. Gradually add the marinade, stirring constantly to prevent lumps from forming. Let the sauce simmer about 5 minutes. Stir in the cream; add lemon juice, salt and more white pepper to taste.

As soon as the fish is done, pour the sauce over it, sprinkle with some chopped parsley, and serve.