While an August heat wave has ushered in an early harvest of grapes for the 1978 vintage, many wine producers in California are anxiously monitoring more than just the late summer weather. A serious shortage of wine bottles now exists in Northern California which has forced several wineries to shut down their entire bottling operations until long-overdue supplies are delivered.

At Napa Valley's Spring Mountain Vineyards west of St. Helena, Michael Robbins said that although labor problems in the glass industry last year have not helped matters, the present shortage of wine bottles is primarily the result of the wine industry's stepchild status in the family of bottle customers. He contends that, in the glass business, the beer industry is favored.

Mary Ann Graf at Simi Winery in the Alexander Valley north of Heraldsburg describes the shortage at her Sonoma County winery as having reached a crisis and reports that the bottling of Simi's 1976 Cabernet Sauvignon is three months behind schedule. "Boycott beer" is her proposed remedy.

Down the road, Souverain's Bill Bonetti has continuously had to reschedule his bottling operations for several months. Winemaker Bonetti says that glass manufacturers have simply taken more orders than they have the capacity to fill. As a result, shipments are months behind schedule and some orders have been canceled altogether.

At Chateau Montelena, near Calistoga, winemaker Jerry Luper terms the shortage "very severe" and notes that his winery's bottling of 1977 zinfandel had to be shut down for three days in late July until more bottles could be secured. Further south, near Rutherford, newly-arrived cases of bottles - stacked nearly 12 feet high - will enable winemaker Neils Venge finally to begin his delayed bottling of Villa Mt. Eden's 1976 cabernet sauvignon.

Although the shortage appears to have greater impact upon smaller wineries than large operations such as Napa Valley's Christian Brothers, a wine subsidiary of one of the world's largest bottlers has been hit as hard as anyone. In early August, Napa Valley's Sterling Vineyards - bought last year by the Coca-Cola Company - was forced to turn off its switches after only half of its 1976 cabernet sauvignon had been bottled. Winemaker Ric Forman is hoping to receive a shipment from a new supplier in Canada by the end of August.

Meanwhile, with the 1978 harvest already underway, the delicate balancing of wine inventories is being made even more difficult.

Last fall, the large Louis Martini Winery near St. Helena suspended bottling operations for more than a month when the supply of bottles ran out. Michael Martini faults the glass industry for not expanding its own production capacity. "They're too cautious," Martini says. "They're waiting to see if the demand for wine continues to grow."

Suppliers may wait too long. Some wineries, such as Martini and Sterling, are already looking to Canada. Others are hoping that a solution will be found closer to home. Michael Robbins suggests that the wineries may have to go into the glass business themselves to assure an adequate supply of bottles for their expanding markets.

Hoping to avoid that, Robbins says that discussions are now underway between winery representatives and a "major producer" in hopes of establishing a new glass factory in Northern California itself. One of the stumbling blocks for any new glass facility, according to Souverain's Bonetti, is obtaining the necessary environmental clearances from state and federal agencies.

With bottling operations behind schedule at many wineries, an unusually early harvest of the 1978 crop is a mixed blessing. But, given the prospect of the first normal harvest in California after two years of drought, no one is complaining.

As usual, California's champagne producers were the first into the fields this year. At Domaine Chandon, the French-owned and directed property near Yountville, the crush of 1978 grapes began in earnest on Aug. 15 - about 10 days earlier than in 1977. About 2,000 tons of pinot blanc and pinot chardonnay grapes will be crushed this year for wines that will not appear in Washington until late 1980.

Other Napa, Sonoma and Alexander Valley wineries began their harvest of 1978 grapes last week. At Spring Mountain, where in-field crushing is practiced, the sugar levels of one lot of pinot chardonnay grapes were actually sufficient for harvesting the weeek before, but the vineyard manager and oenologist were enjoying mid-August vacations and had to be summoned back before the early harvest could begin.

Vineyards in the narrow, northern part of the Napa and Sonoma valleys usually harvest earlier than those in the cooler southern areas. This year appears to be no exception. Sterling commenced to crush its pinot chardonnay on Aug. 23. Some 10 miles to the south, winemaker Bruce Delavan estimated that Stag's Leap Wine Cellar's chardonnay grapes would be ready for harvest during the first week of September. At Simi, the pinot noir were the first grapes to hit the crushers Monday, a full two weeks ahead of their usual schedule.

While an early harvest is not a barometer of quality, indications are that, barring adverse weather between now and October, at least a better-than-average vintage can be expected from the early 1978 crop.