THE BARREL TASTING of '84 California cabernets held here earlier this month was a watershed. It will be looked back upon as a time when California formally entered competition with the Bordelais in wine futures. But the primary source of excitement in the barrel tasting was the wines themselves -- intense, complex expressions of cabernet and merlot that are primarily the product of extraordinary vineyards. There was not a bad wine among the 15 represented, and '84 was an excellent vintage in California.

The second source of excitement was the prices. Not only do the California cabs compete with the best bordeaux in quality, but some represent bargains that are too good to pass up.

Futures in the wines were offered for the first time. The Bordelais have for years sold their wine in advance of release, for what promises to be significant savings for those willing to speculate. Bordeaux futures created a dynamic based on publicity and good recent vintages, turning many casual wine-drinkers into serious ones by virtue of their investments. Now bordeaux is ridiculously overpriced, with the '85 bordeaux futures beyond the reach of the sane and solvent, and California producers wisely took the advice of MacArthur Liquors' Jim Arseneault, who convinced them to sell futures in their wine. If California is wise enough to keep prices reachable, it could profoundly affect the American market.

The wines will not be available until the fall of '87. By then prices probably will have risen significantly, although there is no guarantee of that. Remember, if you decide to buy, that these prices will probably not pertain to the next batch of California '84 futures to come on the market after this "tranche" (slice) is sold. Then you must decide if they still represent real value.

The 15 wineries represented were Caymus; Diamond Creek (Red Rock Terrace, Gravelly Meadow and Volcanic Hill vineyards); Dunn; Girard; Johnson Turnbull; Laurel Glen; Long; Joseph Phelps (from the Backus and Eisele vineyards, and the Insignia blend); Pine Ridge (Rutherford and Stag's Leap vineyards, and the Andrus Reserve); Lyeth; Ridge (Montebello); Santa Cruz Mountain; Stag's Leap (the regular merlot and cab, and the Cask 23); Steltzner; and William Hill. They were all, in a word, wonderful, with a significant dissimilarity in price.

The best deal was the Laurel Glen, a complicated, long-lasting cabernet with great subtlety of flavor, for only $120 a case. Following closely in bargain terms, at the same price, was the William Hill, a lighter, more approachable wine. The least expensive -- but not the least in quality -- was the Santa Cruz Mountain cabernet, with a big cedary nose and lots of good fruit, at only $99 a case.

Prices went as high as $299 per case, but were not necessarily a measure of quality. One of the most impressive wines came from Dunn Vineyards, in Napa, a huge, rollicking cabernet that will last for years but seems to have a concentration of fruit to carry it through. The Dunn costs $180 a case, hardly inexpensive, but a true bargain if you are inclined to spend $400 a case for comparable bordeaux.