Restaurants, mushrooms and babies' names appear to live by the same rules. They mysteriously pop up in clumps. And so it is nowadays with Persian restaurants: Three of them have opened in Georgetown alone. They have similar menus but otherwise are as different as caviar and shad roe. KOLBEH, 1645 Wisconsin Ave., 342-2000. Open: seven days a week noon to 10:30 p.m. Sunday through Thursday, until 4 a.m. Friday and Saturday. V, MC, AE, Choice. Reservations suggested for large parties. Prices: Appetizers $1 to $5, main dishes $4.90 to $8.90, desserts $1.25 to $1.50. Full dinner with wine, tax and tip under $20 a person.

KOLBEH'S MENU makes it easy for people unfamiliar with Persian food: it shows photographs of all the dishes and eases you into your meal with a Persian tabletop salad ar: halved onions, whole scallions, radishes, mods of watercress, cubes of feta and butter, and warm pita to nibble while you wait for dinner.

The style of Kolbeh's black and white tile interior with mirrored ceiling sets it above its Persian neighbors. And the food is good, but not stupendous. Appetizers include the familiar -- hommos, baba ghannouj, stuffed peppers, meatballs -- plus assorted pickles and the three Persian standbys, ashe reshteh (thick lentil and bean soup with greens and noodles), kashke bademjan (saut,eed eggplant with onions, sour cream and mint) and a dull version of salad olovieh (mayonnaise-bound salad of chicken, potatoes, eggs, pickles, carrots and peas). The soup is mild, but grows on you with its dense and tart homeyness. The eggplant, too, has a minty aroma and nuttiness but was flawed by a pool of golden oil.

By the time the main dishes come, you are probably already drinking either salted iced yogurt or the lone wine -- red or white by the carafe or glass. Main dishes are the usual kebabs, their seasonings mild (all of the food was mild, most of it lacked salt, and all was served hot and in generous portions). They had been marinated for tenderness and grilled over a hot fire for crustiness. Only the chicken tasted pointedly of its marinade -- lemony -- and only it was overcooked. Kebabs are accompanied by wonderful Persian rice with butter pats melting into it and with sumac powder to sprinkle over if you ask. The best of the main dishes -- unless unusual specials are available -- is fesenjan, a sweet and thick chicken stew sauced with walnuts and

pomegranate juice in a sweet-tart interplay.

Persian desserts tend toward intense

sweetness, the most cloying of them a lacy squiggle of fried batter saturated with honey.

Kolbeh also has a homey sponge cake and

sometimes a thick, sticky and very good homemade ice cream flavored with saffron and rosewater. The most charming ending: tea in a glass. PARDIS, 3033 M t. NW., 333-2733. Open: seven days a week, noon until 5 p.m.

for lunch, 5 p.m. to 11 p.m. for

dinner. AE, V, MC, DC, Choice. Reservations not necessary.

Prices: lunch appetizers $2.25 to $4.95, sandwiches and entrees $4.25

to $8.95, desserts $1.50 to $2.50.

Dinner apppetizers $2.25 to $5.95,

entrees $7.95 to $13.95, desserts $1.75 to $2.50. Full dinner with wine,

tax and tip under $20.

ALTHOUGH PARDIS'S SETTING is in the Georgetown mode -- cane, chrome and Tiffany lamps -- it still has an Old World family atmosphere. First, service

is friendly though not necessarily knowledgeable or efficient. Second, the menu is broad, ranging from mussels provencal and veal francaise to nargussi (fried spinach with onions and eggs) and khotusht-bademjan (beef stewed with eggplant, onion and tomato). And this is undoubtedly the only menu in town that

promises, "Caviar Take Out Available" Like all the Persian menus, its prices are low. And like all the Persian kitchens, it could use a

little spicing up. That nargussi is a lovely

combination of flavors, but it needs salt and

more seasoning. Salad olovieh is marvelous,

with a tangy dressing. Aush-reshteh is

deliciously tart and creamy, a sparkling

combination of tastes and topped with fried onions. Much of the food, though, including the soup, has been served lukewarm. An upstairs

kitchen seems to be the problem. Main dishes are of mixed success. Fesenjan has been disappointing, its chicken hard and dry, its sauce a thick, sweet mash overreduced and

swimming in oil. Other dishes, such as lamb shank with red currants, are just too mild to be interesting. Kebabs, nearly soft enough to be cut with a fork, show little seasoning. What is

best about the kebab dishes is the rice, dressed with butter and sumac as is usual but

topped with tart pomegranate juice.

There are niceties here -- warmed pita, good Turkish coffee in charming porcelain demitasse cups. But there are desserts achingly sweet,

including a baklava so hard and dry it wasn't

worth the struggle. Of all the Persian restaurants, though, Pardis offers the widest choice of dishes. SHIRAZ

3251 Prospect St., 333-5029. Open:

seven days a week for lunch and dinner 11:30 a.m. to 9 p.m., until 10

p.m. Friday and Saturday. V, MC. No reservations.

Prices: appetizers $1.25 to $2.50,

entrees $5.95 to $8.75. Full dinner with tax and tip under $15. SHIRAZ is a

pretty little restaurant, with sparkling white walls and lace curtains. The small menu is just a few appetizers and a couple of salads; main

dishes are merely kebabs, and, as of my last

visit, there was no liquor license, so the only

drink was herbed yogurt over ice. You could have a whole dinner with tax and tip for under $15. But even so, it isn't worth the money. The eggplant, kashke bademjan, looked like curry -- a lumpy, soupy yellow bowlful -- but

tasted like undercooked eggplant in sour

water, with burned bits on top contributing most of the flavor. The yogurt soup tasted of

nothing but yogurt and cucumber; even the

mint was faint. And the olovieh salad was so

bland even the pickles seemed washed of flavor. The kebabs also were tasteless except

for the lamb, which tasted muttony, and the ground beef, which at least sported some onion

and seasoning. By default, the rice was the

best part of the meal. As for dessert, cubed

farina pudding even looked dreadful, haphazardly hacked up and stuffed in a dessert dish -- and it tasted like solid milk of magnesia.