Open daily for lunch 11:30 a.m. to 3 p.m.; dinner Sunday through Thursday 6 p.m. to 2 a.m., Friday and Saturday until 3 a.m. AE, MC, V. Reservations accepted for lunch, no reservations for dinner. Prices: At both lunch and dinner, appetizers $1.50 to $5, main courses $4 to $10. Full dinner with wine, tax and tip about $15.

Every year or so, to get a sure fix on where the restaurant stream is running, I look into 1825 M St. NW, to see what it is these days. French is long gone. Italian just left. And now it is seafood. Through them all, the bar has seemed to remain packed with all the same happy-hour drinkers.

Sign of the Whale it is called now, and it might be subtitled, "A Seafood Pub."

While I never managed to find out what is packing them in at the bar, I could readily see what is the draw in the small dining room in the rear: low prices. This is one of the rare restaurants with the same prices at lunch and dinner, and even for lunch they would be considered restrained. The Maryland Crabcake Platter is $5.75. That's for two large crabcakes with a mountain of french fries and a little dish of coleslaw, plus tomato and cucumber slices.

A lot of food for the money, especially when it is seafood. The reason it is possible may be that it is not very good seafood--the crabcake tastes like a competition between filler and bits of shell --but I have certainly had worse at considerably higher prices.

Most of the people around me at dinner were eating similarly mountainous platters of soft-shell crabs; but since the season was ending it seemed pointless to sample them for readers' benefit (and if they continue to be available, you might be wary of their having been frozen). Otherwise, the entrees on the standing menu are fish and chips--not bad, actually--a couple of steaks (the top one being $10 for 12 ounces), salads and sandwiches. The menu makes a lot of its hamburgers, with toppings such as guacamole, bacon, cheese. But the hamburger is worried into toughness by whoever handles it, overcooked though crusty, and a disappointment through carelessness rather than by design (the viciously salty mushroom sauce that garnishes some of the hamburgers is worse than careless, though). For $3.75 to $4.50 you've had a better hamburger.

More interesting, there are several daily specials. And if the chef would only cook the salmon more gently and forget the b,earnaise if he can't make it right, the $7.50 salmon steak would be one of this town's great buys. On Mondays when lobster is left over from the weekend, it is the other of this town's great buys, at $6.50 for a one-pounder with potato and vegetable. The lobster is likely to be a bit watery, and not the most plump and sweetest one, but some restaurants do no better at three times the price. In general the daily special platters are less than $6, although if stuffed sole with crab ($6.25) is an example, quantity and price are considered the crucial features of the food.

Too bad, because it wouldn't take much more for the baked potato or fresh zucchini to be less waterlogged. Or the fish to be less dry. But, in addition to overcooking, one of the typical errors of mediocre seafood restaurants is that they swamp everything with sauce or seasoning or butter. Thus, oysters Kirkpatrick are drowned in chopped vegetables and tomatoey broth, though the oysters and their bacon topping are no problem. One day the green beans--fresh ones--were gasping in a sweet sauce. A hamburger was murdered by too much and too-acrid blue cheese.

Soups are another matter: hopeless. Lobster bisque has endearing little bits of lobster, but in a particularly unpleasant-tasting and starchy broth. Mushroom soup was mushroom halves in what appeared to be plain sour cream. Odd. And Nantucket Seafood Chowder, though agreeably stocked with pieces of soft-shell crab, tasted like undiluted canned cream of something soup.

Two assets compensate. The french fries are cut from fresh potatoes with their skins on and are well made, though at lunch I found them cold and hard, as well as fishy from overused oil. The onion rings, fat and fresh, are also good, and the $2.50 batch is enough to serve a tableful of folks.

Appetizers are priced out of proportion to the main dishes: $3 to $5 for most of them. The specials, the few desserts (among them one day a nice, homey chocolate cake) and the wine specials are the values at this restaurant. On my last visit, for $9.50 you could have a choice of Geyser Peak '78 chardonnay or Piesporter Goldtropfchen '79 riesling kabinett.

In all, Sign of the Whale is not much of a restaurant; most of its space is devoted to the bar, though the small back dining room is pleasantly decorated with whale art, and there are tablecloths even at lunch. The service is as eager as the singles-hopping at the bar. But dinner for under $10 downtown is a rare enough occurrence that it is worth knowing about, particularly when the food is real--the vegetables fresh and the main dishes actually made from scratch. Just remember that homemade is not necessarily well made.