There may be a summer slowdown elsewhere, but in Bordeaux, one of the major centers of the wine world, the summer of '77 promises some drama and tension because there is such uncertainly wine supply and prices.

The frosts that struck French vineyards in late March and early April did considerable damage in Bordeaux, Cognac and the region where muscadet is produced. While dire predictions of a lack of white grapes in all three regions appear to be true, growers of red grapes in Bordeaux have taken heart with the flowering of the vines. The overall damage appears to be less severe than originally predicted, though some vineyards - particularly those heavily planted with merlot grapes - were hard hit.

As a result, classified growths from the 1976 vintage are again being offered for sale, at prices about the same as the 1975s. That may seem astonishing in light of limited quantity. But reports on the market from three firms, Gilbey's, Sichel and 21 Brands, provide some perspective.

Assessment of the 1976s fairly consistent. "The reds are rich, supple and fat, but have little tannin, and in some cases, are rather, short, lacking in power," stated the unsigned Gilbey's bulletin. Whites made from grapes harvested before the September rains should be best, but "there are large numbers of wined of inferior quality in this category" and "it is unlikely the quality of the sweet wines of 1976 will be good."

"The red wines are ripe, often with good color, have low acidity but lack concentration," wrote Peter Allan Sichel. They "will mature quickly and provide pleasant wine with elegance and character. But the variation is considerable . . . There vineyards with a high proportion of old vines and a consequent lower yield have produced wines of real quality." Unlike 1967, "there was virtually no rot in 1976; there grapes were healthy and so too are most of the wines."

Nonetheless, the wines opened at 1975 opening prices and were almost totally withdrawn from the market during the period between the frost and the flowering. They won't reach U.S. retail stores until 1978, but what happens now determines their eventual price and may effect the stability of the market.

Red Bordeaux sales increased 32 per cent last year. (White Bordeaux sales have been declining and the reds are now in the majority, a reversal of the post World War II balance.) The U.S. market for both types turned upward in spectacular fashion last year. The increase in reds was from 455,000 casese to 915,000; for whites it went from 147,000 to over 300,000.

American wine merchants are the most outspoken in warning against price rises and raise the spectre of a collapse in the market similar to that of 1972. But from the reports it is clear that, for the moment at least, the United States is not the significant factor it was in 1972.

The growers who produce the ordinary wines of France are in trouble, but Americans don't buy much vin ordinarie . Most of what is shipped to this country is appelation controlee , the top quality wine. Yet one of every five bottles of wine drunk in France is now of appelation controlee quality (as opposed to a ratio of one in 17 in 1950). The French and Belgians have become very good customers of Bordeaux and so far they haven't complained about prices. Meanwhile Burgundy has upped its prices sharply, so has Beaujolais. Both areas are recovering from inferior vintages in 1975.

Gerald Asher contends the uncertain political climate in Franch has promted growers to hold onto their wines, considering the wine more secure than cash. Sichel points out that the expansion in appellation controlee vineyards since 1950 has not begun to rival the expansion in sales.

Gilbey's bulletin predicted "there will be only moderate interest" in the 1976s at 1975 prices. "In view of the large volume, a lesser price would have a greater chance of success in a market that has already bought a large percentage of the 1975 vintage obviously a great classic year." That was before the frost. Also before the frost, Sichel wrote, "They will prove right (for asking high prices) if the 1977 vintage is poor in quality or quantity."

Thus there isn't much moaning about the setback the frost dealt expectation for a large harvest in 1977 and there is talk of developing brand name blends to give a lift to the sagging white wine arm of the industry. Nor are the French growers listening very carefully to the warnings of a buying downtown being shouted across the Atlantic. The negotiants, those who buy wines for export, haven't done very well in the boom in classed growths, according to Gilbey's. With the 1975 vintage, for the most part they "have acted merely as brokers," making only minimal profit.

Nonetheless, boom beats bust and after three consecutive years of upturn, there is now a "contract" committing the trade to upper and lower price limits in relation to supply and demand. Gilbey's claims the market has stablized and that price levels will "develop in accordance with normal inflation." According to Sichel, "Things only got out of hand when 'institutional' money was thrown at the market in vast amounts. This is not happening now." Asher feels that considering cumulative inflation, the early Bordeaux prices were "not bad. There's lot of stock though," he added, "and people are not beating down doors to get it."

That's enough to cause some internal tension, no matter how cheerful the trade's exterior communications.

Those interested in following the progress of the 1977 crop in Bordeaux may do so by dialing in on weekly reports sponsored by Dreyfus, Ashby, a subsidiary of Schenley. The two-minute report often includes market information. The toll-free number is 800-223-9716.