Open Monday through Friday, 11 a.m. to 10 p.m.; Saturday, 5 to 10 p.m. MC, V. Reservations. Prices: Full-course dinners about $5 to $8; a la carte platters at dinner $4 to $9.50.

SOME restaurants are problem-solvers. The problems: Where do you take Aunt Vera from Toledo, who likes a nice place where the food is familiar and the surroundings dignified? Where do you take dad for Father's Day if you want a restaurant that looks important but does not cost a lot, since he is ultimately footing the bill? Where does a high school student go for dinner on a date, a place that impresses but doesn't send one scurrying for a foreign dictionary or a bank loan?

Carmack's is no strain. Neither the menu nor the price is a threat, the food is reliable if not outstanding, and the surroundings have sufficient pomp to impart some elegance to the excursion.

Carmack's is a surprise. Down a spiral staircase from a glass extravaganza of an office building lobby, it is a Williamsburg transplant. The cluster of small rooms with low ceilings is sufficiently authentic that you expect to be able to look through the deeply set mullioned windows onto the village green rather than into the next room. One room resembles a tavern, another the dining room of a Colonial burgher. And from the muted Colonial tints to the candles on the mantels to the appropriately scarred wooden tables, the tone is real enough that you begin to believe that the Colonial home actually did have electric fires in its grates. On the tables are solid-looking Colonial utensils, tall stemmed glasses, and more tall white candles. Here and there are grand Chinese bowls filled with flowers. The costumed waitresses seem to have been schooled in the patience of a Colonial housewife and the speed of Paul Revere.

After the gracious setting, the next surprise is the price. Complete dinners, the likes of short ribs or trout amandine with appetizer, two vegetables, dessert and tea, average $6 or $7. A la carte main dishes (which include dessert) are more, but none more than $9.50, half under $7. Here is that rare enterprise, a handsome restaurant where you can dine with some wine or a drink on less than $10.

You dine on something simple, most likely on something good. To start, a soup that is undeniably homemade - and well made - or the usual shrimp, herring, crab cocktail, fruit cocktail or hospital-bland chopped liver. The best is yet to come.

My best was crab imperial, claimed by the menu to be Carmack's famous recipe, determined by my sample to be a matter of very good lump crabmeat unsullied by little but mayonnaise in moderation and a faint touch of green pepper. The kitchen had learned the secret of crab imperial: success depends on using fine crabmeat and doing very little with it. It is a lesson applied to advantage elsewhere, too. The fried shrimp are neither battered too heavily nor cooked too long; corned beef hash at lunch was too finely chopped, but had the homey taste of just corned beef, potatoes, onions, and not too much else. On the other hand, somebody tired too hard with the London broil, went too far, after broiling it rare and slicing it just thin enough, by overdressing it with canned mushrooms and an outrageously salty sauce. The meat alone would have yielded more satisfaction. The menu goes on to steak, roast beef, shish kebab, a few more seafood dishes and main dish salads; an educated guess would steer a diner towards the simplest. Experience would also steer a diner to concentrate on cooked vegetables. The "Carmack's bean salad" is indistinguishable from anybody else's bean salad, but the creole eggplant or summer squash, thick with tomato sauce and slightly sweet, spiked with onion and green pepper, is a far, far better vegetable dish than most restaurants serve hereabouts. Any day the menu offers six or nine vegetables, perhaps acorn squash halved and baked in a sweet sauce with a ginger scent, maybe buttered fresh asparagus. There are people who still care about vegetables, and those people should know about Carmack's.

Other accompaniments are accorded less attention. The bread - french rolls cut into small chunks and pumpernickel both dry and dull - is a letdown. The house wine is Almaden, the rest of the wine list neither distinguished nor notably moderate in price (though there is an Almaden Rhine for as little as $3.50). Desserts are limited to what the menu bills as "Carmack's Superb Cheesecake" (the waitress confided it was bought elsewhere), ice cream or a soft, barely sweetened baked custard and a very sweet, also custardy bread pudding with plenty of raisins. Nostalgia in a bowl.

Carmack's does nostalgia well. It leaves your Aunt Vera feeling that is has been a nice meal.

Hard Sell for Soft Drinks - The hostess at Hamburger Hamlet, in giving you the bad news about how long you will have to wait for a table, suggests you have a drink while you are waiting. What she does not tell you is that a soft drink from the bar costs 60 cents, whereas nearly twice as large a soft drink at the table costs only 50 cents.

Bargain Bar - The Falls Church Inn calls it a salad bar, but I call it a full meal - soup, roast beef, ham, cheese, salads from tossed to marcaroni, applesauce, and a couple of desserts. You can make a submarine sandwich or build a chef's salad. And all that costs only $1.75, Monday through Saturday, 11:30 a.m. to 5 p.m. That's a generous definition of lunchtime, too.

Going on the Peanut Standard - One could be justified in wondering who would spend $8 for two pounds of peanuts. But that one could not have tasted peanuts from the Williamsburg Peanut Shop, the crunchiest peanuts in recent memory. And now one doesn't have to add the expense of a trip to Williamsburg; they are also at Capitol Hill Wine and Cheese.

Ringing Up the Change - Being on Capitol Hill, even a little restaurant like 209 1/2 couldn't get away with having no public telephone. So, doing everything with a flair, that restaurant put in telephone jacks at the tables. And, being like-wise committed to running a solvent business, the restaurant charges fifty cents for the use of a tableside telephone. Outrageous price for a call? Then make five - for the same price.

Diners' Guide to the Chef's Own Homemade Grade A Fresh-Picked Truth - When service is slow, pull out your copy of "Truth-In-Menu," a free booklet available at Emerson's & E.J.'s and any other restaurant that asks to stock it. You can learn about your rights and restaurants' wrongs while you wait for your "fresh" (frozen) shrimp, your "8-ounce" scrawny hamburger, or over-mature "spring" lamb - then send it back to the kitchen.

Table Talk - It was in a Georgetown French restaurant that the diner asked the waitress what tripe was. "I think it is some kind of European fish," she answered, adding, "I don't know; I'm from Virginia." The diner then suggested the waitress ask the chef, but the waitress declined, explaining that the chef was French and therefore temperamental. But she did try to be helpful in describing the tripe as "like corned beef - you have to develop a taste for it." The diner ordered the tripe and decided she couldn't develop a taste for cow's stomach linings, so she got her money back but not her dignity.