In one respect, it's an unfortunate coincidence that both Bordeaux and California had very good vintages in 1978. Over the next 10 years, the temptation to hold comparative tastings of the clarets, on the one side, and the California cabernets and merlots, on the other, is going to be irresistible. Nevertheless, I am one of many who does not approve of international taste-offs as a way of evaluating wines. It's the apples and pears principle: They do not taste the same.

Having said that, honesty will out: There is some similarity of style between the two set of '78s. The better wines of both regions have a good, deep color, still showing the purple edge of immaturity, with plenty of fruit in the mouth but not overly tannic. Well-balanced, they finish with an astringency that indicates potential elegance.

These '78s should be of particular interest to the growing band of red-wine drinkers who incline to the impatient infanticide of their cellars. The wines do not require excessively long cellaring. The Bordeaux are more approachable now than those of 1975, and will mature between the '76s and the '75s in from five to 12 years, depending on the specific chateau.

Early tastings of the California cabernets indicate a suppleness that is closer to their '75s than the very firm '74s, but that have the richness and pepperiness of the earlier year. The winemakers believe the '78s will mature in five to 10 years.

Having had a cool, wet spring and an equally damp start to summer, the Bordelais consider themselves lucky to have had a good vintage at all. Theirs was a small crop and the Washington wholesale and retail trades are now vying to acquire what is available this spring. Americans did not rush into buying futures in the winter of '78-'79 mainly because prices were continuing the upward spiral that had started in 1976 and because our pipelines were full, with the classed growths and petits chateaux of '75 and '76.

Now, buying is brisk. Prices have held steady or dropped a little as the French sell bottled stocks to make room for the much larger '79 vintage and as the dollar has strengthened against the franc. A wide range of better quality chateaux are available now and more will be on the shelves by early June.

Prices vary, depending on the number of middlemen. Those retailers who have imported directly are offering the best prices, but, as quantities are small, you should find out when those in which you are interested will be on sale. Here are average retail prices of several chateaux: First growths: Margaux, $40 per bottle (back to form, at last); Latour, $50; Haut Brion, $45. Other classed growths: Leoville LasCases, $22; Pichon-Laland, $22; La Lagune, $19.

The quality of the '78 merlots from California is an much of a pleasant revelation as that of the cabernet sauvignons. Two beauties are Stag's Leap Wine Cellars and Clos du Val, both from the Napa region, and about $12 each. As deep in color and full in body as the cabernets, they have a very attractive combination of smoothness and earthiness that will be enriched over the next five years or so.

The most interesting cabernets are in the $10 to $15 range. Don't be disturbed by the many new names on the shelves. Have fun and experiment. Price is not necessarily a quide to quality. One fine example is the Pine Ridge (Rutherford District, Napa), which, apart from having a very pretty label, is at an equally pretty price of $8.