Which came first, the chicken or the egg? Are there so few Indian restaurants in this country because people aren't interested in Indian food? Or are people not interested because there are so few restaurants?

Chicken or egg, Indian food hasn't achieved the customers needed to take off in popularity. Is it its legendary hotness? Tex-Mex and Szechuan put that theory to rest. A reluctance to try the new and strange? Our growing fondness for sushi makes that hard to believe.

Whatever the barriers, Indian restaurants in this area remain relatively scarce--a handful of biggies downtown, and a scattering of storefront operations in the suburbs. Here are a couple of the latter, more than worth a visit. INDIA INN

929 N. Glebe Rd., Arlington. 522-6750.

Open for lunch Monday through Saturday 11 a.m. to 2:30 p.m., for dinner daily 5 p.m. to 10:30 p.m. AE, MC, V. Reservations recommended. Prices: Dinner appetizers about $1.50, entrees $3.95 to $7.95. Full dinner with beer or wine, tax and tip about $14 per person. Beer and wine only. India Inn may be a storefront, but it's an unusually pretty one, pale-walled and austere, and it has amentities-- china, silverware, carpeting. Prices are low.

Be sure to have appetizers. The meat- and vegetable-filled samosas are big and puffy and served with a wonderful mint-pepper chutney. Even better and more unusual are shami-kebab, meat and lentil patties cooked with fried egg, and vegetable cutlet (which tastes far better than it sounds), a delicately fried patty with an intriguing cumin-coriander-pepper flavor. One of the very best entrees is murg botti, a variation of the traditional lamb botti kebab, in which chicken morsels are marinated in a light, fragrant, tart sauce, then baked. Two more common dishes, both good, use tender lamb chunks, well trimmed and marinated. In rogan josh, the lamb is cooked in a velvety, sweet-tart yogurt sauce with whole peppercorns, and in lamb sagwala it's accompanied by spice-permeated spinach. Murg bulai is chicken cooked in a pleasantly tart cream sauce, like an Indian version of a good chicken fricassee. Vegetable curries are good, if unexceptional, but beware the heavily oversalted daal. Biriani dishes, in which lamb, beef or chicken are cooked with rice and a complex spice mixture, are disappointingly flat here, lacking flavor and textural contrast.

An unusual series of dishes called ''karahi" are served sizzling in an Indian wok. They're simple and superbly done-- chicken, beef or lamb stir-fried with tomato, green pepper and spices. Among the three breads, the deep-fried puri has too much excess oil, but the skillet-fried paratha is excellent. Unusual in an Indian restaurant are the three Afghan dishes. Bulanee, fried turnovers stuffed with ground meat and vegetables, are marvelous, golden-light pillows about eight inches across-- gargantuan compared with the ones usually served in Afghan restaurants--accompanied by a sauce made with velvety homemade yogurt. Aushak, also very good, are big, chewy dumplings topped with spicy ground meat in a yoghurt-mint- scallion sauce. The third Afghan offering, shishlik, has been disappointing, the cubes of meat overcooked and oversoft for a grilled dish.

Dessert? Ras malai, a cheese dumpling in a sweetened cream sauce, is something like a small mound of very fine-textured ricotta with a faintly casein-like flavor. It's an acquired taste that's well worth acquiring. Come to think of it, that's the point with Indian food. To make the effort is to open yourself up to a whole new continent of tastes. NATRAJ

1327-F Rockville Pike, Rockville. 340-7373.

Open 11:30 a.m. to 9 p.m. daily. Cash only. Prices: $1.20 to $3.95 per dish. Full dinner with wine or beer, tax and tip about $7 per person. Beer and wine only. Located in an all-but-hidden little shopping center, Natraj is a storefront restaurant with paper plates, plastic forks and beer that's served in a waxed paper cup. A not-too-energetic ceiling fan is all that cools the air. But Natraj is one of the few places left where two people can eat for about $12. And eat very well indeed.

Among the appetizers, known as "savory snacks," the standouts are gol-gappa and papri-chaat. The former, crackly hollow spheres of very thin fried dough, are punctured by the diner and stuffed with a mixture of chickpeas and potatoes in a slightly hot, sweet-tart sauce, and further flavored with a delicious tamarind-mint chutney. Papri-chaat combines flat pieces of fried dough with chick peas and potato, all in a wonderful mixture of yogurt and fruit chutney, swirling together on the plate in hot-sweet counterpoint. (The similar dahi- bhalla is far less interesting.) Puri and paratha, the fried breads, can be good one day and a sodden ooze of oil the next, so you're safer with the baked chapati. Masala dosa--thin, lentil flour pancakes filled with onion, potato and spices--are top-notch here, beautifully delicate and without the sour-milk flavor that characterizes some dosas. Curries are pleasant, but nothing special, and tandoor chicken will be far too dry for most tastes. The best meat choice, a beautifully flavored dish, is chicken tikka, cubes of marinated chicken coated with spices and cooked long and slowly. What's available for dessert depends upon what Jamak Arora, the owner-chef, has made recently. Pinni, when she has them, are a must--dense balls of sugar, coconut and raisins, with a delicious interplay of textures and flavors. (Laddu, somewhat similar, is more floury and somewhat monotonous.) Jalebi, a sugary, fried flour filament is mainly just sweet, but worth a try.

Natraj has just five tables, and Arora works virtually alone. How will she cope with more than a few people at a time? Maybe those whose last names begin with A through D should go on Monday, E through H on Tuesday, and so on. Or maybe we could have a lottery. The winner would go to Natraj.