An unusually cool summer and a wine workers' strike made the prospects for 1980's California grape harvest less than rosy. But, with the strike settled and a sudden heat wave, those sour appraisals have sweetened considerably.

Although some winemakers expect lower crop yields than normal -- and others express only guarded optimism about their product's quality -- some predict surprisingly good wines for the 1980 vintage.

"We have some wines we're looking forward to being super-duper," said Ed Friedrich, who is winemaster and general manager at Sam Martin winery in South Santa Clara County.

Wines that Friedrich places in that category include Pinot Noir, Sauvignon Blanc and Charonnay.

But he also estimated the yield for the central coast area would be down 40 to 50 percent, with the yield of Pinot Noir off 55 percent in the Santa Clara Valley. Production of Zinfandel and Sauvignon Blanc, however, probably will be normal, he predicted.

"The Chardonnay," said Daniel Mirassou, vice president of marketing at Mirassou Vineyards, "looks at this point that it could be the best we've ever had." But he also predicted a crop "30 to 35 percent" smaller than normal.

The recent heat wave "is just simply marvelous," said Faith Greaves, director of publicity at Almaden Vineyards. "It is bringing the sugar on rapidly. At the same time, acids are remaining abnormally high and this is good for balance. We are really tickled at the whole thing."

Greaves predicted better-than-average quality, though she estimated yield would be 10 to 20 percent lower than last year, which, she added, was an especially good season.

Others in the industry were cautious, saying much of the crop has yet to be harvested and sudden cool weather -- or worse, rains -- could hurt slow-ripening grapes, such as cabernet sauvignon, and zinfandel, which produce California's best-known reds.

Another problem mentioned by several winemakers is that, with the warmer weather in the last week or so, many grapes have ripened so quickly the winemakers are having trouble processing them fast enough.

Because the hot weather "snuck up on everybody," Fredrich said, "not everybody has prepared to take grapes off and some grapes are overripe."

"The constant tone of agriculture is guarded optimism," said Brian St. Pierre, media director for the Wine Institute, the trade association for the state's winegrowers.

He said it is too early to judge quality in most cases, but added, "If this weather keeps up we could have a pretty nice year. It's just the kind of weather we've been waiting on."

Winemakers, however, became worried last month, after several consecutive months of cool weather, that their profits would be dampened.

Lower-than-normal temperatures caused some vines to form small bunches of grapes -- and the bunches were fewer than usual. The cool weather also raised concerns that some grape varieties might not reach maturity.

On the other hand, an extended hot spell might not be beneficial either, according to Mirassou. "When the weather gets over 100 degrees for very long," he said, "the maturity of the vine or grapes don't really take place."