HEADING NOW toward the end of that long airless tunnel known in Washington as "summer," the morning rush-hour mixture of bus fumes and cologne hanging so heavy in the air they can almost see it, Washingtonians have long ago tired of the nightly ceremony that begins "I don't know, what do you want?"--and ends with tuna salad.

Now is the time to cash in on the rule of culinary psychology stating that if something looks beautiful and orderly, people think you worked on it for days.

Here are four recipes for "composed" salads, meaning only that you have taken several ingredients, probably mostly vegetable, and arranged them on a platter in a way that looks, well, composed. The composed salad most people know is the salade nicoise, that combination of potatoes, tuna, anchovies, beans, eggs and tomato, the precise composition over which latter-day Escoffiers love to bicker.

A composed vegetable salad makes an ideal accompaniment to grilled summertime meats. With the addition of a little sliced or julienned salami or more substantial vegetables such as beans it can also be a wonderful one-platter summer meal. It can be as simple as alternating rows of tomatoes, potatoes and egg slices with a mustardy vinaigrette or, on days when you are feeling particularly creative, as complex as the nouvelle cuisine predilection for fashioning birds in flight out of raw leeks and carrots.

Dressings are another source of variation, from plain vinegar and oil to vinegar and oil spiced with anchovies and herbs to mayonnaise-based mixtures such as aioli (garlic mayonnaise).

Other hints:

* In composing a composed salad, don't feel constrained by convention, or by these recipes. The idea is to use what you have or can get without trekking all over town.

* Salad can be arranged on a platter large enough to serve everybody or on individual plates.

* Leafy green lettuce makes a nice backdrop for everything, especially if you have a white platter.

* Cook vegetables just until they are barely crisp-tender. The dressing will continue to "cook" them if they marinate in it for any length of time.

* Vary shapes. For instance, you can julienne some vegetables, slice others, leave others whole.

* Match dressing to salad ingredients. For instance, save stronger dressings such as anchovy or aioli for earthier ingredients like chick peas or peppers. Potatoes seem to go well with every kind of dressing.

* If your salad looks drab and you were going for art, remember black olives and red things like peppers or tomatoes. They add color to any salad without changing its character substantially.

* Cut cold roast meat or chicken in strips, marinate in dressing for an hour or two, and arrange with the vegetables for a one-platter meal.

* Vegetable platters with the addition of sliced salami or prosciutto make a lovely antipasto or a full-fledged family meal.

* A partial list of possible ingredients: beets, asparagus, snow peas, zucchini, potatoes, tomatoes, hard-boiled eggs, dried tomatoes, black or green olives, baby lima beans, fava beans, green beans, chick peas, green, red and yellow peppers, fennel, cucumber, sliced salami or other cooked sausages, scallions, thin slices of (or diced) red onion soaked in cold water for an hour or two to remove harshness, artichoke hearts, hearts of palm, fresh herbs with their flowers. SHRIMP, SNOW PEA, POTATO AND BEET SALAD (6 servings as a main course) For dressing: 3 tablespoons lemon juice 1 tablespoon fresh or preserved tarragon, or 1 teaspoon dried 2 small shallots 1 hard-cooked egg yolk (optional) 1 cup light olive oil 1/3 cup heavy cream Salt and pepper to taste For the salad: 1 pound snow peas 2 pounds or more shrimp, cooked, shelled and deveined 6 small beets 8 medium potatoes 1/2 cup white wine Leaf lettuce

To make dressing: In the bowl of a food processor place lemon juice, tarragon, shallots and optional cooked egg yolk (it will help to smooth out and thicken the sauce), and process until blended. With motor running, add olive oil in a thin stream. Remove dressing to a bowl and blend in cream. (If you do this in the processor you may end up with butter.) Add salt and pepper to taste.

If you do not have a food processor, chop tarragon, shallots and optional hard-cooked egg yolk, then add lemon juice and beat until blended. Beat in olive oil in a thin stream with a whisk or fork, then stir in cream and seasonings.

Blanch snow peas in a large quantity of boiling salted water for one minute. Drain and refresh under cold water. Moisten with a little dressing and chill.

Boil unpeeled beets gently in salted water to cover until just tender. Peel and slice thinly, then cut into matchstick-size pieces (julienne). Moisten with a little dressing and chill.

In a saucepan, cover unpeeled potatoes with cold water and bring to a boil. Cook gently until just tender. Peel and slice. While still warm, add white wine to potatoes and toss gently. Let stand at room temperature.

An hour or so before serving time, mix shrimp and potatoes separately with enough dressing just to moisten. Chill. At serving time, arrange lettuce leaves on a large platter, then arrange salad ingredients in separate piles in any design that pleases you. Serve extra dressing on the side. BEEF, WHITE BEAN AND VEGETABLE SALAD WITH MUSTARD VINAIGRETTE (4 servings as a main course)

This salad makes a quickly-prepared family meal. Leftover broiled flank or other steak works especially well. For the dressing: 1/4 cup good wine vinegar 2 teaspoons dijon mustard 3/4 cup good olive oil Salt and pepper to taste For the salad: 2 to 2 1/2 cups leftover beef 2 small shallots, minced 2 to 2 1/2 cups canned cannellini beans 2 to 2 1/2 cups mixed julienned raw vegetables (see below) Lettuce leaves

In a small bowl, whisk together with a fork the mustard and the vinegar. Add olive oil in a thin stream, whisking constantly. Adjust seasoning.

Cut beef into thin strips and toss with half the minced shallots and one-third of the dressing. Let marinate in refrigerator. Drain cannellini beans and rinse under cold water to remove thick juices. Let drain thoroughly. Toss beans with the other half of minced shallots and one third of the dressing.

Cut raw vegetables into matchstick-size pieces and toss them together. One good combination is red peppers, green peppers, carrots and celery. Other possibilities: yellow peppers, snow peas, green onions, seeded and peeled cucumber, radishes. Obviously, the more colorful the better. Toss vegetables with the last third of the dressing. Let ingredients marinate anywhere from half an hour to all day in the refrigerator, or the salad can be served immediately.

Arrange salad on lettuce leaves on four individual plates, beef in the middle, beans on one side, vegetables on the other. TUNA AND PEPPER SALAD WITH ANCHOVY DRESSING (4 servings as a main course) For dressing:

4 tablespoons wine vinegar

2 cloves garlic

2 scallions

1/4 cup parsley tops

4 anchovy fillets

2 teaspoons fresh, minced thyme, or 1 teaspoon dried

2/3 cup good olive oil

A pinch of cumin

Salt and pepper to taste For the salad:

3 tablespoons olive oil

4 to 6 sweet peppers, preferably green, red and yellow

2 cloves garlic, chopped

2 tablespoons chopped parsley

2 15-ounce cans chick peas, drained

6 hard-cooked eggs

3 7-ounce cans solid white tuna packed in oil

Black olives and/or strips of sun-dried tomato for garnish

Lettuce leaves

To make the dressing, combine vinegar, garlic, scallions, parsley tops, anchovy fillets, thyme and seasonings in a food processor and process for a few seconds. With motor running, add olive oil in a thin stream and process until sauce is smooth and thick. Adjust seasoning. If you do not have a food processor, chop garlic, onions, parsley and anchovy fillets. Add vinegar and seasonings, then whisk in oil gradually.

For salad: Wash peppers, then dry. Remove seeds and slice in strips about an inch wide. In a large saute' pan heat olive oil. Saute' pepper strips gently until they just begin to soften, about 8 minutes. Sprinkle with chopped garlic and parsley and cook another minute or two. Do not let peppers get too soft.

Mix chick peas with a little dressing. Arrange chick peas, tuna, eggs, peppers and garnish on a bed of lettuce. Drizzle a little dressing over tuna and pass remainder. VEGETABLES WITH AIOLI (6 servings)

Served with a little leftover cold roast chicken or pork, this makes a fine end-of-summer meal. For aioli: 2 to 8 fresh, firm cloves of garlic 2 egg yolks 1 cup light olive oil Lemon juice Salt and pepper For vegetables: About 5 cups of barely cooked, bite-sized vegetables, such as 1 cup each of green beans, yellow string beans, artichoke hearts, chick peas and zucchini, or broccoli, cauliflower, peas, beets and potatoes

To make aioli, mash garlic cloves (how many you use is strictly a matter of personal taste) to a paste with a little salt in a medium bowl. Anchor bowl on the counter by wrapping a dampened towel around its base. Add egg yolks and whisk lightly. Begin adding olive oil drop by drop, whisking gently but constantly. As sauce begins to thicken, oil can be added in a thin stream. When all oil is added, add a few drops of lemon juice and salt and pepper. Adjust seasoning. If sauce seems too thick, add a few drops of very hot water to thin it out.

Vegetables should be slightly warm when they are mixed with aioli. If necessary they can be reheated in a slow oven. Mix each warm vegetable separately with the sauce, then arrange vegetables on a platter. Serve immediately.