Just as soy sauce is the fundamental ingredient in Chinese and Japanese cooking, fish sauce is added to nearly every dish in Southeast Asia. Or, if it's not in the dish itself, it's the base for a dipping sauce.

Fish sauce can take some getting used to for those who haven't grown up with it. Trying it has been likened to encountering camembert for the first time, a comparison that is not as far-fetched as it seems. The aroma, stronger than the taste fortunately, is more like an odorous cheese than aged fish.

Called nuoc mam in Vietnam, nam pla in Thailand, tuk trey in Cambodia and ngan-pya-ye in Burma, fish sauce is made by packing fish, usually anchovies, in barrels or crocks, covering them with brine and allowing them to ferment in the tropical sun over a period of months. As with olive oil, the first "pressing," from which flows a clear amber liquid, is the best.

Fish sauce was known in the western world long before the influx of immigrants from Southeast Asia. The ancient Romans doused almost everything with liquamen (or garum), made from anchovies and other fish in much the same way as Southeast Asian fish sauce. This kind of fish pickling is still seen in Italian dishes that get their heady fragrance from anchovies packed in salt. As the Romans knew, fish sauce is highly nutritious. Rich in B vitamins and protein, fish sauce and rice were the K-rations that sustained the Vietcong.

In Southeast Asia, the flavor of fish sauce is complemented wonderfully by the fresh tastes of lime juice, basil, mint, ginger and chilies. A couple of tablespoons are added during the cooking just as salt would be in the West. The finest fish sauces are reserved for the sweet dipping sauces that are familiar to anyone who has visited a Thai or Vietnamese restaurant, though they go easy on the fish sauce in deference to western palates (and, for this reason, are sometimes a little too cloying). Besides sugar, these are seasoned with lime juice or vinegar, minced garlic, fresh chilies and often grated carrot, and they accompany fried foods such as the popular "imperial rolls."

The very finest fish sauce is said to come from Phu Quoc, an island off Vietnam, and this has come to be something of a generic name for top quality. Most available here come from Thailand, and the rest from Hong Kong, China and the Philippines.

Avoid fish sauces, or any sauces for that matter, packaged in plastic bottles. As might be expected, fish sauce requires no refrigeration, and keeps indefinitely.

*In spite of the East-West experimenting that is going on, fish sauce has been little tried in western cooking, although as one of the world's most versatile sauces it certainly should be. One could start with it as a salt substitute in salad dressing (Caesar salad often uses anchovies), or in marinades, barbecue sauces, or with foods where you might ordinarily flavor a sauce with anchovies.

THAI CHICKEN WITH MINT, BASIL AND PEANUTS (4 to 6 servings)

1 large whole chicken breast

1 egg white

1 tablespoon cornstarch

1/2 teaspoon salt

1 cup plus 2 tablespoons peanut or vegetable oil

1 cup raw peanuts

1 tablespoon minced garlic

1 tablespoon minced ginger

10 small or 5 large red chilies, seeded and cubed

6 scallions, white part only, cut into 1/2-inch lengths

1/2 cup fresh mint leaves

1/2 cup fresh basil leaves

FOR THE SAUCE:

2 tablespoons fresh lime juice

3 tablespoons fish sauce

1/2 teaspoon salt

1 1/2 tablespoons sugar

1 teaspoon Thai or Chinese chili paste with garlic

Skin and bone the chicken breast. Cut the meat into 1/2-inch cubes and mix them in a bowl with the egg white, cornstarch and salt, and refrigerate for 30 minutes or more.

Heat 1 cup of oil in a wok or sauce pan. When hot, turn off the heat and add the peanuts. When they're light brown, remove to a paper towel and set aside, leaving the oil in the pan.

Combine the garlic, ginger, chilies and scallions, and set aside, and put the fresh herbs together. Mix the sauce ingredients. Reheat the cup of oil and add the chicken cubes, stirring to separate. When they change color, after about 2 minutes, remove to a colander to drain.

In a clean wok or skillet, over high heat, add 2 tablespoons oil, then add the garlic-ginger mixture and saute' for 30 seconds. Add the sauce, and when it boils, add the chicken cubes and fresh herbs. Cook, stirring until most of the liquid is gone. Transfer to a platter, sprinkle with the peanuts and serve.