WE WERE spoiled by those 1970 clarets. When tasted in the first months after their arrival, we were treated to round, generous mouthfuls of astonishing fruit. Of course, the wines were young, but they were balanced and harmonious. And in the succeeding months they stayed steady; they did not deceive. All we had to do was wait until they matured to greatness.

Well, the '75s aren't behaving that way at all. Take Ducru-Beaucaillou for example. From May to August of last year, it revealed fullness on the palate, great depth of character, and savory, complex flavors. But since then, the wine has cloaked its charms, showing only a rather unsophisticated fruitiness that one finds in the likes of Hawaiian Punch.

Pichon-Lalande has displayed even more versatility. It tasted of mint in April; pungent, hard and cedar-like in May; smooth, savory, superlative in August; and downright dumb in December. Which of these is the real Pichon Lalande?

Of course, any experienced taster has realized that one's impressions of the same wine may differ from time to time. However, the differences shown by the '75 clarets cannot be ascribed to such subjective considerations. They are too dramatic, too obvious. In mid-1978, for example, Montrose had a huge, expansive bouquet; now it has next to none. Whereas Lascombes once gave a balanced impression with distinctly minty overtones, the mint has given way to fruit while harmony has turned to discord. Even the intensely fruity flavors of La Lagune have, on occasion, hidden themselves only to reappear. And after a slow start, Haut Batailly is finally showing its expected quality.

If anything of general utility can be gleaned from current tastings of the '75 clarets, it is the knowledge of the various ways in which a wine may be completely dumb. Young Montrose generally provides a good illustration. On the other hand, a wine may be selectively dumb, perhaps revealing only one quality while suppressing others.

When a wine is selectively dumb, as was Ducru-Beaucaillou last fall, it is most vulnerable to misunderstanding. Better that a wine be completely dumb, virtually yielding nothing to the senses, for one may then be inclined to defer judgment. Unfortunately, for those with limited experience, a single tasting of a selectively dumb '75 claret may lead to erroneous evaluations.

What does all this mean for the consumer? First, those who purchased a case of a particular claret on the basis of its reputation and who then found the wine disappointing on first tasting need not panic. It's not the wrong wine, just the wrong time. Second, this is simply one more reason not to rely too heavily on currently published guides or tasting notes.

The erratic development of the '75s should not cause us to hang up our tasting glasses in despair. Such development is not unknown to students of Medoc and, in fact, was predicted for the '75s by some astute observers even before they were bottled. Rather than base an evaluation of particular '75s on a single tasting, one should taste and retaste so as to chart their undulating progress. By experiencing their peaks one will better understand their valleys.

My conclusion, based on the extensive "movies" I have been taking of the '75 clarets, is that this vintage does show definite quality. In this vein, it has already become common to compare the prospects for the '75s with the performance of the most highly regarded vintages of the recent past. My impression is that although the '75s do not show the fruit of the '70s, the finesse of the '66s, or the concentration of the '61s, they do display greatness in a style all their own-one of complexity, substance and depth.

But to me as a wine consumer, it is more relevant to know how the '75s compare with the '79s and '80s than with any prior vintage. The answer to that question will have a greater impact on the desirability and price of the '75s than anything else. For it is already clear that at a minimum the '75s are the best vintage since 1970 and-except perhaps for a few remaining bottles from that great year-are the finest clarets on today's market.