"Riesling," wrote Frank Schoonmaker in his "Encyclopedia of Wine," is "one of the greatest of white wine grapes, apparently a native of the Rhine Valley . . ."

In the United States, it is also one of the most confusing among wine names. The grape that is made into the glorious wines of the Rhine and the Mosel and the stylish, more austere rieslings of Alsace, is usually identified here as Johannisberg or white riesling. "White" is the proper name, but the public prefers to buy "Johannisberg," so both terms are used.

In addition, there are others on the market, among them gray riesling, emerald riesling, "riesling" that is really sylvaner. Furthermore, under current wine law, only 51 per cent of any riesling bottle need be riesling. Lesser grape types may be blended in.

"Although many different white varietal wines are available from the leading California wineries." Alexis Bespaloff wrote in his useful "Guide to Inexpensive Wines," "many of them are comparatively neutral in style. Part of the reason is that certain varieties do not have a clearly defined taste, and part is the intent of some wineries to make clean white wines without much varietal character. Consequently you may find several well-made California chablis to be as attractive as many varietally labeled wines - and less expensive."

There is, nonetheless, a fascination with varietal wines (those carrying the name of a specific grape or grapes) as they are assumed to be a step up from the American generics (blend with amorphous names such as chablis). The appeal of white varietals has been heightened by the so-called white revolution, strong/consumer demand for white, or colorless, wines and liquors. The most prestigious white wine grape is the chardonnay. Next comes the riesling. Yet chardonnay wines are rarely available under $3. Riesling, with its spectrum of contributing grape types, is sold in a wide range of prices. There is a further complication. While chardonnay wines invariably are dry, rieslings may be bone dry or as sweet as quality wine can be. The famous auslese wines of Germany are rieslings that have been infected by botrytis, the "noble rot." They develop enormous concentrations of natural sugar and are made into dessert wines that have the smell and taste of nectar.

Making these sweet wines is an expensive process. Grapes must be hand-picked; there is a great sacrifice to juice to the mold and therefore a substantial reduction in volume. Furthermore the mold doesn't thrive in every vineyard nor during every vintage. Until recently, most California winemakers have avoided the noble rot as much as possible and consequently lacked experience in making auslese wines.

The generation of young winemakers is fascinated by them, however, and as there has been considerable botrytis in California during the past few harvests, wines in this rich style are coming on the market. They may bear the designation "late harvest," or "from selected late harvest grapes" or even B.A. or T.B.A. These last terms come from German designations beerenauslese and trockenbeerenauslese. The California wines have similar sugar content.

In "The California Wine Book" Bob Thompson links gray riesling with sylvaner, traminer and emerald dry as wines in a "slightly off-dry, drink now style," Steamed clams, crab or fried chicken would be suitable food matchups, he suggests. Turning to Johannisberg riesling, Thompson calls it "one of the great learner's wines of the world," yet adds, "the character . . . is complicated enough to sustain a lifetime of exploration.

"Good though it is," he continues, "California Johannisberg riesling must be liked on its own terms or not at all. Occasionally there is a haunting kinship between a California Johannisberg and Alsatian riesling, though this is unpredictable. A vaster gulf separates Californians from the Rhenish relatives. And a still vaster separation lies between Californian and Mosel wines.

"Rhines and Mosels grow with less heat and less sunshine than the coolest, cloudiest districts of California afford. In favorable years the German wines come home at 10 to 11 per cent alcohol. Californians run 12 to 13 per cent as a matter of course."

Lacking California's hot sun, Eastern winemakers have hopes they can do a better job of producing German-style rieslings. High alcohol is an enemy of delicacy in flavor and bouquet.

A spectrum of rieslings was presented recently to a tasting panel organized by The Washington Post. The wines were purchased in local retail shops and hidden in bags so that no one knew the identity of the wine being tasted. While the emphasis was on California, a popular German riesling, Schloss Vollrads, and an economy-priced riesling from Alsace, Charles Jux, were included.

The Alsace wine displease most of the 11 tasters. The German wine was favorably received in general but it is far from the most distinguished representative of its area and was found wanting in character. The sharpest divergence of views was over a wine that turned out to be Paul Masson's Emerald Dry, a runaway winner of the value-for-money prize. "Sugar water," said the most outspoken critic. The entry from Chateau St. Jean, a small, extremely quality-oriented vineyard in Sonoma County, caused considerable controversy as well.

In general, rieslings should be drunk within one to three years although the sweeter, late harvest wines should improve in the bottle and last longer.

Tiny bubbles were observed in several wines. Called petillance, these bubbles are the result of vinification and in no case were strong enough to give the wine a sparkling or spritzy quality. There was considerable variance in colors and taste, with sugar/acid balance being a critical factor in individual reactions to each wine. (To taste complete and appealing, the sugar and acid contents of a riesling should offset each other. If sugar dominates the wine is fat and candy-like, if acid dominates the wine is tart and leaves an unpleasant aftertaste or "finish.")

In the chart that follows , the name of the vineyard, the vintage ("N.V." means non-vintage), price, score and a synopsis of comments is given. Scoring was done on a scale that would award 20 points for a "perfect" wine. The scores shown are the average for each wine. Some negative remarks have been included to help explain the ratings. To the extent comments are contradictory, they show divergence of view.