Open for lunch Monday through Saturday 11 a.m. to 3:30 p.m., Sunday noon to 6 p.m. No reservations. No credit cards or personal checks. Prices: platters $4.25 to $5.25, desserts $1.90 to $2.25.

It's too cold to stand in line for a hot dog on the Mall. And the Rodin exhibit at the East Building of the National Gallery may be a bigger draw than Santa Claus this season. So it is time for a reassessment of the cafes at the National Gallery of Art.

There are three places to eat in the gallery: a cafeteria and the Cascade Caf,e on the bottom floor of the main building and the Terrace Caf,e two flights up in the East Building.

I'd opt for the Terrace Caf,e. But so do many other people, and it is the smallest of the three, so don't expect ready seating. Its advantage is that it is away from foot traffic, yet is in full view of the Calder mobile, the skylights and the Rodin statuary at the entrance to the exhibit. No Parisian outdoor caf,e could offer a more glorious view. Its greige Formica and wood tables, rough-textured beige carpet and golden brown leathery banquettes are soothing, offering a nice break from gallery-hopping. And the menu--this month molded around a Rodinesque French caf,e theme--includes a hamburger with such toppings as bacon, cheese, avocado and mushrooms. It's hard to go wrong with a six-ounce, cheddar-topped hamburger.

The Cascade Caf,e's advantage is, obviously enough, the wonderful waterfall that provides its backdrop. Its disadvantage is the noise; the rush of water is a pleasant sound, but overlaid by the flow of people between the buildings and captured by the low metallic ceiling and the bare marble floor, the clatter at lunchtime is at least distracting, sometimes deafening. Effervescent or irritating, it depends on your mood. Still, it is a brightly attractive room, especially when populated by the wonderful variety of gallery-goers, from artists to babies carried in pouches by their mothers.

The menus of the two cafes are nearly identical, but the Cascade Caf,e offers an omelet (cheddar, mushroom or reuben) instead of the hamburger, and chicken in wine-cream sauce instead of the Terrace Caf,e's veal-chicken-pork.

Unlike the Rodin exhibit, the caf,es' food will neither offend anybody nor excite anybody. Such dishes as beef bourguignonne, pasta salad, p.at,e and cassoulet have been reduced to their most common denominator. Wine sauce that a child would not find too strong. A sausage and bean casserole the provides only the merest hint of earthiness. One guest at lunch recognized the beef bourguignonne as something a mass-circulation women's magazine might call "New Ideas to Dress Up a Hearty Beef Stew."

It is the kind of food you would expect from a menu that offers a choice of country p.at,e or cottage cheese on its fruit and cheese platter.

It's certainly not bad food, just bleached of character. The p.at,e would make a good meatloaf sandwich; it is compact, lightly seasoned, homey but lacking flavor. The cassoulet is served in what looks like a Corningware casserole; its chicken and veal are hardly pungent meats to perk up white beans, and they are dry from such long cooking. The sausage tastes as if it had been blanched, but the crumb topping is nicely browned. It is not a casserole to savor, but it's not likely to offend anyone either; it tastes like a beany version of chicken pot pie. Pasta salad is kind of a chef's salad with noodles instead of lettuce, its bed of green and white noodles covered with segments of diced cheddar, diced ham and diced turkey. A few spinach leaves tucked under here and there, a couple of pale tomato wedges on the side, the whole accompanied by a little paper cup of creamy dressing. Oh, well. But the salad comes with pita bread split and toasted with grated cheese; many will find it impossible not to nibble their way through the entire basket. Beef bourguignonne provided a close parallel in impact: plentiful cubes of beef in a slightly gluey but inoffensive dark red sauce, that offered few mushrooms and none of the pearl onions we expected. The bacon-strip was an odd alternative to the usual method of cooking the casserole with bacon. I'd sum it up as a filling break from the world's artistry. The omelet--overcooked but well-stuffed with saut,eed fresh mushrooms--was equally adequate.

I encountered one remarkable note amidst this culinary monotony: the small salads that accompanied the platters. After my encounters with countless soggy and oversweetened salads in the mass-feeding stations of this country, I was astonished to find the caf,es' salads so good. The caraway cabbage salad that arrived with the cassoulet was as good a coleslaw as I have tasted; its onion and caraway seeds did not overwhelm the cabbage and there was no sweetness to detract from the refreshing flavor. The cucumber and lettuce salad with the omelet was crisp and lively, its creamy dressing nicely tart. The garden salad basilic with the beef bourguinonne lacked dressing, but the dice of tomatoes, cucumbers and peppers with basil was crunchy and fresh tasting.

The most impressive change about the caf,es from past years is the personable and helpful attitude of the waitresses. No stony and irritable institutional waitresses, these. They are willing to offer suggestions or to ask questions of the kitchen, make you feel welcome and handle your order efficiently. They even take the trouble to point out that ordering two glasses of wine at $1 each is a waste when an entire carafe costs only $2.30.

While we haven't found espresso available, though it is on the menu, the caf,es serve aperitifs, beer, soft drinks and quite decent coffee (75 cents). They also merchandise desserts well, showing the pastries (from Watergate, we were told) on rolling carts. Drinks and desserts are priced high in proportion to the main dishes, probably to make it worthwhile for the caf,es to allow people to linger at a table with just a cup of coffee or a piece of pie. There have been plans to serve a special dessert menu in the afternoons, from 3:30 to 4:30 at our last check; and one of the promised offerings is an ice cream soda to be called a Haagendazsoda.

The pastry trays are well-tended, a big advance over times when they have been left half empty, picked over and unattractive. But by now you must be familiar with Watergate pastries. There is also a good warm apple cobbler, tart and fragrant. The sleeper among the desserts, however, is a hot fudge sundae made with Haagen-Dazs ice cream and a dense bittersweet fudge sauce. It would offer a happy ending to a holiday outing.