Following three successive years of meager harvest (1978 yielded the smallest crop since 1969), the 1979 "vendage" has corks popping from Reims to Epernay. Although it will be several weeks before the exact qualtiy of this fall's crop can be measured, it is already being hailed as at least a very good commercial vintage. "Similar to 1979," says Michel Medard at Moet and Chandon, the regions largest producer.

The harvest began on Sept. 25 and has continued under good weather conditions. Barring any unwelcomed rains, the harvest should be completed by Oct. 19.

September also brought to completion the extended merger negotiations between Pommery and Lanson, two of France's leading champagne firms. Under the agreement, reached in late August and revealed last week, the principal shareholders of Lanson will control two-thirds of the Pommery stock. The shareholders of the new group have expressed an intent, however, to maintain the "personality, tradition and autonomy" of each of the two houses.

Bill Deutsch of Somerset Wine Company in New York, which imports Pommery to the United States, considers the merger to be a beneficial move for the two producers. "Pommery," he says "brings to the marriage certain old-line traditions" and a philosophy of exclusivity. Its production and, correspondingly, its export allocations are small and its focus is on the international premium market. Lanson, he adds, is more aggressive and, because of certain corporate ties to Florida and other factors, focuses more on the growing American market. Deutsch sees such mergers as an inevitable response by French producers to rationalize their operations in an effort to control escalating production costs.

Despite this fall's apparently copious harvest, champagne prices are expected to continue to bubble upward. Respected producer Christian Pol-Rodger believes this year's increases will be no less than 15 percent, but not as dramatically sharp as in the past 12 months. While all French wine prices have shot upward in the latter half of the 1970s, even non-vintage French champagne now commands the premium price of $10 a bottle in most Washington retail stores.

Interviewed at his cellars last month in Epernay, the youthful Pol-Roger attributes some of the expansive worldwide demand for champagne to changing habits of consumption. It is, he said, increasingly being served in Europe and America as an aperitif and/or with main courses, in addition to its traditional role as a "festive" beverage with which to toast a special occasion.

"Curiously," he added, "this change necessitates greater reliance on the kingly chardonnay grape," which grows principally along the Cotes des Blancs, southeast of Epernay. The harvest of chardonnay grapes accounts, unfortunately, for less than half of the region's annual production. Between Reims and Epernay, picturesquely hugging the hillsides of the Montagne de Reims, and also along the Marne river valley west of Epernay, the balance of the region's 60,000 cultivated acres are planted with pinot noir and the lesser-regarded pinot meunier grape.

But Pol-Roger and others, such as Virgile Portier at Beaumont-sur-Vesle, believe Americans pay too much attention to vintage champagne. Many producers -- especially smaller ones like Portier -- strive to establish a consistent, identifiable style in their non-vintaged champagne which can be relied upon from year to year dispite the vagaries of the weather of northeastern France.

Pol-Roger is also convinced that American consumers do not allow sufficient resting time for champagne following the agitation of trans-Atlantic shipment. Most producers in France cellar their wine a minimum of six months following disgorgement. ("Disgorement" is the last step in the production process where accumulated sediment is removed prior to final corking.) Even so, he says, the wine needs several months of lateral rest following its journey to permit small amounts of dissolved carbon dioxide gas to be replenished.

This resting period is not to be confused, however, with an aging process. Although connoisseurs are divided on the question, Pol-Roger and most experts believe that champagne does not improve with age. If stored properly, however, vintage champagne can survive for five to 10 years after its release.

A long lifespan is not predicted, however, for the 1973 vintage, described by Pol-Roger as a "light but fresh, clean wine." While some bottles from other vintages can still be found in area shops (such as the very good 1971), the 1973 will be principally featured during the remainder of 1978 and through next year.

While American demand for vintage champagne continues to extinguish available supplies, the sobering truth is that American annual consumption of champagne is only one-fifth that of the English and only one-eightieth that of the average Frenchman, who consumes almost two and one half bottles per year.