Bangkok's Orient Hotel is a culinary world all its own

When you arrive at Bangkok's Oriental Hotel, an extraordinary blend of style, tropical splendor, and literary associations awaits you. Joseph Conrad stayed here, as did Somerset Maugham and Graham Greene. There are suites named after them at this hotel on the banks of the Chao Phraya River, the river of kings.

Thailand, a country of lush, fertile lands, produces wonderful fruit year round.

Rose apples - pear-shaped, and three inches long - are like the juiciest pineapple. These the Thais eat with a little salt.

There are fresh litchis. And there are the rambutans, small hairy ovals that, with the husk removed, offer a translucent fruit with a delicate, almost opalescent quality.

But fruit is just the beginning. Thailand is rich in delicacies flavored with chili, jasmine, tamarind, garlic - hot, sweet, salty, spicy. And the Oriental, more resort than hotel, is a culinary world all its own.

At the Normandie, an elegant French restaurant atop the hotel's older wing, the exquisite dishes arranged recently by French chef Louis Outhier of L'Oasis in La Napoule, France, made impressive use of fish. Salade de Pla Kapong, a warm nouvelle cuisine concoction, used local fish, a crab pate, king prawns with vegetables, and medallions of pork with mango.

Fish, however, is the center of all attention at Lord Jim's Restaurant in the new river wing.

The vistas of river traffic are accompanied at lunchtime by a lavish buffet - soups, sushi, and local tuna.

On the regular menu are whole charcoal-grilled pla kapong, the legendary fish from the Gulf of Siam, or pla kapong in a salt crust, baked in the oven. There are lobsters from the southern island of Phuket, succulent crustaceans that are best simply grilled.

But the gastronomic highlight of a visit to the Orient - and, some knowing Asia hands say, to Bangkok - is a visit to the D'Jit Pochana Restaurant. Across the river from the hotel, it has an outdoor branch where the Thai specialties make your mouth water in anticipation, and the biggest problem is what to choose.

On a hot night, with the promise of rain and just enough breeze to ruffle the tablecloths, you sit and watch the rice barges move slowly upriver.

You begin with Pla Goong, spicy shrimps cooked with lemon grass, hot pepper, and lime; Po-Pear Tord, fried spring rolls stuffed with pork and clear noodles served with a rich, sweet plum sauce; and on to some remarkable soups.

There is Tohm Yum Goong, a fragrant clear lobster soup seasoned with hot pepper; Tohm Yum Pla Dook Yarng, a smoked catfish soup; a chicken soup with coconut milk, heady and rich, called Tohm Kak Guy; and a rich seafood hot-and-sour soup called Poh Tak.

As a distant crackle of thunder brings the cooling rain closer, you go on to Gun Chieng Poo Tord, fried snow-crab claws; perhaps some crisp smoked or fried shrimp, squid, or catfish; or mushrooms or asparagus. There are a dozen curries, a dozen chicken dishes. There are dishes of roasted duck curry, dishes of rice birds, noodles, and the fat, stuffed omelets that are Thai favorites.

At the end, the sweets: Salim, soft noodles bathed in sweet coconut milk; or Sahm Sae, a collection of bejeweled jelly, nuts, and preserved fruits in syrup; and, of course, those marvelous fresh fruits.

Thai food and some of the exotic fruits are increasingly available in the United States, both in restaurants and food shops.

Here is a recipe from the ''The Original Thai Cookbook,'' by Jennifer Brennan (Richard Marek Publishers, New York). If fresh litchis are not available, canned may be substituted. Melon balls also make an attractive substitute. Litchis in Custard (Leenchee Loi Mek) 5 eggs, separated 5 tablespoons granulated sugar 1 1/2 cups unsweetened evaporated milk 15 to 20 fresh litchis, peeled, or canned, or melon balls

Whisk egg whites until soft peaks are formed. Place in a sieve and steam over a pan of boiling water until firm. Set aside.

In a saucepan, beat egg yolks and mix in sugar and evaporated milk. Stir over low heat until it becomes a smooth custard. Remove from heat.

Place fruit in serving bowl. Add custard. Spoon egg-white foam over custard. Refrigerate and serve. Serves 4.