SOME neighborhoods just sit around for years waiting to be discovered, but when they hit, they hit big. So it is on Capitol Hill, with new restaurants auditioning from Union Station to the Marine Barracks. In the past couple of years, Massachusetts Avenue NE and environs has starred the Gandy Dancer, La Ruche and the Man in the Green Hat. On Pennsylvania Avenue, 209 1/2 and Yolanda's have followed Ali Baba, Machiavelli, Toscanini, and the A & K reincarnated as Taverna the Greek Islands. Now, farther southeast, four restaurants have opened. Two are still too new to review: Thursdays, upstairs from Mr. Henry's at 6th and Pennsylvania SE, is said to specialize in "music and cuisine"; La Casita of Capitol Hill, 723 8th St. SE, is a branch of the immensely popular hole-in-the-wall TexMex La Casita of Arlington. Two other establishments, around just long enough to have established a following, represent the variety the Hill can accommodate. The Broker

713 8th St. SE, 546-8300.

Open Monday through Friday, 11:30 a.m. to 2:30 p.m.; Monday through Saturday, 5:30 to 10 or 11 p.m. AE, MC, V. Reservations.

Prices: Dinner main courses $6.75 to $11, sandwiches $4.25 to $4.95. Lunch main courses $3.95 to $6.95.

The absences make the heart grow fonder at The Broker - the absence of dining room cliches like paintings on the walls and plants hanging in air. If you have never understood how less could be more, The Broker is the place to learn. An old plumbing shop has been transformed, mostly by leaving the right parts intact. The walls have been scraped down to beautiful old brick. The arched windows have been left to section off the space. And what looks like it might have been an alley is now a skylighted dining alcove. Nothing distracts from the light and space and brick patina except a few driftwood branches, unpolished pale wood tables, columns softened by unassuming drapery, and sprays of miniature lilies or giant alliums. Chairs are capacious and comfortable. Taped music meanders from pop to classical. The menu, too, is pared down to ten main dishes at dinner, a few sandwiches and a salad added for late supper, bracketed by some of the most original appetizers and desserts inside the beltway.

The menu is Swiss, which means slightly German and faintly Italian with a bit of French and hamburgers. Strictly Swiss are the melted cheese dishes - raclette with boiled potatoes and pickled onions, and fondue with dippers of vegetables, ham and chicken as well as bread; each of the cheese specialities is served for a minimum of two people, unfortunately. Less familiar but also typically Swiss is air-dried beef served as an appetizer with an inexplicable garnish of prosciutto (very good prosciutto, to be sure). Those are straightforward, simple dishes; there are higher mountains to climb.

You may have had snails in shells or snails in mushroom caps, even snails in puff pastry. But the Broker flatters snails by wrapping them in chicken breasts and setting them on croutons to soak up their garlic butter. They never wore better. And who cares about authenticity when the Country Pate turns out to be a butter-smooth liver mousse that could be an understudy for foie gras.

Some things are too good to last, among them the elaborately served Swiss Souffle Emmenthaler Bread, a souffle-shaped, heavily cheesed freshly baked quick bread that occupies an entire waiter for an entire five minutes to present and serve it - the production alone being worth the $1.25 price.

Stuck as one might be on appetizers and bread, eager as one ought to be for dessert, one traditionally orders a main course in between and, if you don't have someone to share the raclette or fondue, you are limited to eight choices from the menu and whatever daily specials there may be. Besides steak - grilled or tartar - there are seafoods with zucchini, eggplant and tomatoes, crabcakes disappointingly made with shredded king crab and heavily flavored with pimento, and the best of the seafoods, shrimps livened with garlic breadcrumbs and surrounded by a pale pink sherried cream. The Italian part of the menu is chicken breast with herbs, green peppers, pimentos and potatoes. The best dish sampled was veal, small shavings of pale meat in a nutty-flavored mushroom cream sauce, a dish of delicacy. The greatest letdown was the Wellington, not a filet of beef, but ground beef compact and overcooked, a waste of one of the best pastry wraps to be found locally. I hate to recommend ordering a dish just for its crust, but that is the only reason for considering this dish.

The Broker is a restaurant to suit many moods, and people come dressed for a gala or in T-shirts, come for a quick sandwich or a long evening, sit at the long tile bar or at quiet, well spaced tables. The service lulls you, envelops you, tempts you with descriptions of sauteed rosti potatoes and Moet et Chandon still white wine. When they are attending elsewhere, though, it is difficult to capture the waiters' attention, since the space is so large.

In all, the restaurant is a display of creative energy that sometimes falls flat but maintains an overall appeal. Nowhere is the energy more apparent than in desserts. The Fancy Torte is a bombe of bavarian cream laced with brandy and liqueurs, layered with sponge cake and a wonderful crunchy nutted cookie. TO vie with it are a tart lemon torte frosted with an elegant buttercream, a too-dense chocolate seven-layer cake, and hot apple crepes that are but an excuse for their delightful warm custard sauce.

Renovated plumbing shops don't come cheap these days, so tuck your credit card into your T-shirt pocket. Most appetizers hover around $4 at dinner, and main dishes around $8. With $2 for dessert, you should plan to leave about $25 a person behind after you have drunk and eaten what tempts you. You won't regret it if you have ordered carefully and taken into consideration the taste of the surroundings as well as of the food. Coolbreeze's

507 11th St. SE. 543-3184.

Open Monday through Saturday, 10 a.m. to 11 p.m.; Sunday, 11 a.m. to 4 p.m. No credit cards. No reservations.

Prices: Sandwiches 95 cents to $2.75. Platters average $4.25 to $6.50.

"It is the waiter's personality," explained our waiter when we commented on the brisk business at Coolbreeze's. He had pulled up a seat to lounge on as he took our order, this bearded young man who probably needed a rest after successfully charming babies in strollers and elders who drifted off to another world between bites.

Coolbreeze's is a neighborhood bar with a hardworking amateur cook sending sausage sandwiches and linguine downstairs via a dumbwaiter to the dining rooms - one with blue checkered tablecloths and long benches, the other slightly fancier, with red checkered tablecloths.

Well, it is more than a neighborhood bar. Firest, there is the vase with a sngle snapdragon on each table. There are the paintings - for sale - on the walls. There are the half-timbered and knotty pine wall sections, the yellow iron lanterns, the blackboard listing the specials - green noodles with bacon and cream, scampi, rhubarb pie. The scribe can't spell, but by the end of the evening some customer will have corrected the most glaring errors.

There is the garlic bread that accompanies the food - not the best of garlic breads, but a nice gesture. There is the anti-pasto salad which is added to your dinner for only 45 cents - a graceful arrangement of rolled Italian cold cuts interspersed with olives, peppers, cheese and egg on lettuce. Even the salad that comes free is a generous mix of olives, mushrooms and cheese with the greens.

This is the kind of eating place where one day the rice is the best part - buttery and peppery - or the freshly cooked carrots. Another day the bracioli is the thing to have, being highly spiced rolls of beef with a well herbed and onioned tomato sauce on linguine.

Pasta is usually on the menu, and usually it is too flabby to be respectably Italian, but fills you for less than $5, maybe with sausage or meat balls or bacon and cheese topping it. Scampi have their good days, lightly floured and sauteed with garlic and parsley, but $6.50 puts them at the top of the menu.

Don't expect such niceties as freshly cooked turkey in the chef's salad or quality French bread on the French bread pizza. Soups are homemade but not necessarily well made, and the home-baked pies and cakes are merely passable, though the rhubarb pie shows promise.

Coolbreeze's is an easygoing place to get a lot of food at little price, to satisfy all the cravings of your group when they range from an egg and pepper sandwich to chili to spaghetti and meatballs to beer - with TV in the back room or rock music in the front room. And, as much as anything, it is the waiter's personality . . .

What to Do With the Rest of the 50-Minute Hour - The American Cafe is serving a ten-minute lunch to about one luncher in ten. The arrangement is that the restaurant guarantees to serve a cup of soup and a roast beef sandwich within ten minutes of its being ordered at lunchtime (Monday through Friday, noon to 3 p.m.), or the meal will be on the house.That doesn't include the waiting in line, being seated, and having the waiter arrive, but that, says the restaurant's manager, usually takes less than five minutes.

More Crain With Less Salt - Long have there been complaints about the Greenery's policy of refusing to serve a piece of bread, instead selling nothing less than an entire bread basket. New management has taken over, and the man in charge promises, "During my regime that kind of thing will not occur." Whether the customers want a piece of bread or more cream or whatever, "They would get it with a smile," and no charge. Good news also includes a new menu, an expanded kitchen, and a new restaurant next door, to be called Whiskers, opening late this year.

Streets' Eats - Washington is progressing from its hotdog-and-ice-cream street food restraints. On the 2400 block of 18th Street NW, right in front of Fields of Plenty, you can now buy freshly fried felafel - cumin-spiced chick pea fritters - stuffed into whole wheat pita with lettuce, tomato and tahini [sesame sauce]. This great gooey walkaway sandwich costs $1.30, and can be washed down with ginger beer or lemonade, both homemade with honey and spring water, or freshly squeezed orange juice. Jimmy's Felafel Stand promises to be open daily, 11 a.m. to 6 p.m. or later, at least until the end of September.

They Tried That With Wines, and It Didn't Work - The Booeymonger at Wisconsin and Jenifer NW, found it too confusing to call people by number when their orders were ready, so they started calling last names. Again, problems. The help couldn't pronounce the last names. So now they call out people's orders by first names, offending many customers, at least those over about 12 years old. It may start a new American restaurant fad. Instead of, "Hi, I'm Sam, your waiter," we may begin to hear, "Hi, I'm Peggy, your diner."