For 120 OF America's most enthusiastic wine investors, it was extremely difficult to swallow. Yet, the international wine authorities were nearly unanimous in their advice last March at the most expensive one-day seminar and tasting ever held in this country. Except for a tentative dissent from the romantic Michael Broadbent of Christie's in London, the consensus opinion was: "Do not invest in wine, at least if you expect your future financial yields to outpace Wall Street." Alas, a bottle of 1929 Chateau Latour may be nectar from the gods; it is not, however, a Rembrandt.

Despite this sobering appraisal of the financial limits of investing in wine, there was no rush by the collectors assembled from 18 states and abroad to cash in their "liquid investments." Nor were there any leaps from the Windows on the World restaurant's 107th floor by those who participated in the lavish bacchanalian fest, sponsored by the Manhattan restaurant and by the Wine Spectator newspaper. Moreover, as New York oenophile Dr. Marty Katz sagely observed, while it may not be Saudi Arabian real estate, owning a wine celler confers a cetain sociability, a certain "mystique" that transcends profitability. To that, Michael Broadbent did not dissent.

Katz had good and bad news for the wine investors present, whose personal cellars averaged over 1,000 bottles of wine. The "bad" news was that wines made today in France and elsewhere are not "structured for longevity" as were the great clarets of the 19th century. "While many of the wines of the 1870s were not even drinkable for 30 to 40 years and are enjoyable still, most of today's wines are drinkable very soon and may not even last 30 to 40 years." Unlike the limited, aristocratic wine market of the 1870s, today's market demands earlier-maturing wines to satisfy expanding world demands. This shift, which Katz suggested has intensified since World War II, does not please wine "investors" -- who prefer intense, tannic, long-lived wines such as the 1945 and 1961 clarets.

In the continuing battle between the "collectables" and the "consumables," the "good" news is that today's great wines can indeed be consumed much earlier. Moreover, by purchasing magnum-size bottles -- in which the wine matures more slowly -- and in buying selectively from "great" vintages on "futures," such as the 1975 clarets, wine collectors can still maximize their investment opportunities. Katz cautioned against buying wines older than the excellent 1945 vintage unless the collector knows how the wine has been stored, and then buying only those with healthy color and "ullage" (the airspace between the cork and the wines), which indicate that the wine has not over-oxidized.

In his "hottest" tip, Katz joined subsequent speakers such as Christopher Stevens of Cognac, France, in predicting that the next greatest investment opportunities will come from Australia. "They are developing 'boutique' wines, he noted, "that will become very collectable." Katz further encouraged investors to seek out collectable wines from Italy and Spain, and he had high praise for California's cabernet sauvignon and the late harvest riesling. Regarding "consumables", he favored the 1967 and 1971 clarets for present consumption.

Ken Onish, vice president-wine for Seagram & Sons, Inc., agreed with Katz that California cabernet has been a sound investment, but warned that investors should move quickly to bolster their positions in California wines, as rising prices for premium chardonnay and cabernet wines threaten to eliminate California as the world's bargain basement for collectables. The next release of BV Private Reserve cabernet is forecast to exceed $300 a case.

Having just returned from Bordeaux, Onish is particularly hopeful that European resistance to the 1978 clarets will cause prices for the abundant 1979 clarets to remain stable or even dip slightly. He says that the 1979 vintage is indeed better than generally reported and that the 1979 pomerols are actually better than their 1978 counterparts.

Onish terms the still moderately-priced, reasonably-available 1975 clarets as excellent investment choices, particularly since the "lesser" 1978 and 1979 vintage clarets are 20 to 30 percent higher in price. But without question, his "insider's" tip is to buy the cru bourgeois wines from proven chateaux in good years such as 1978. In his view, these wines, often averaging half the price of the classified growths, represent an excellent strategy for investing in wines that will mature nicely within 10 years. With improved technology and more careful vinification, many of these wines (such as Greysac, Phelan Segur, Mevney) from the Rhone Valley are, he believes, the best red wine values in France today. And for undifferentiated value, Onish is absolutely convinced that German premium white wines ("mit pradikat") are splendid bargains.

Whether participants in the novel seminar-tasting got $245 worth of information or enjoyment from the one-day enological orgy may be open to question. What is clear, however, is that the sponsors had to return the checks of over 200 wine buffs for whom there was no space. Encouraged by that kind of response, they have scheduled a "wine weekend" in New York for Oct. 16 to 18, 1981; and similar "investment" seminars are being planned for Chicago, Texas, and California.

The days of the $10 wine tasting may never be seen again.