THAT SOUND you heard from Paris the other day, at the congress of the French Communist Party, was the drop of a second shoe. The first dropped a year ago when the Communists, having abandoned their joint program with the Socialists, suffered a calamity at the polls on the way to what at least some of them had hoped would be the road to power. A long sorting out culminated this week. Party leader Georges Marchais announced the decision to end the six-year partnership with the Socialists-and thereby to return to the strategy of going it alone and forgo the chance for power.

More is involved than the fortunes of one party in one place. Taken together with other European developments, it marks the decline, though perhaps not the demise, of "eurocommunism" as a major force threatening or promising (take your choice) to redraw the political map of Europe and to turn the whole East-West contest pracitically inside out. It is hard to believe that as recently as two years ago serious people on both sides of the atlantic, comtemplating what seemed to be the inexorably rising fortunes of communist parties in France, Italy and Spain, were debating nothing less than the ultimate fate of the West. The idea that free societies could actually choose communism had intruded upon the consciousness even of those repelled by it. Questions of defensive strategy were widely and hotly discussed.

But the center has so far held. In Italy, the Communists have ended the policy of cooperation with the government is, though they remain, of course, a formidable force. In Spain, the party rather quickly reached a modest plateau. In France, various elements in the party resisted the compromises in program and political style that an alliance with the Socialists required, fearing that the price of coalition and especially of victory would be too high in loss of ideology and tradition. The turn taken the other day returns the party to the open ideological and financial dependence on the Soviet Union which was its norm in the past. Party leader Marchais seems at heart so much the Stalinist it is easy to believe he is glad to be back.

Two years ago some people were hoping, and others expecting, that a communist party would be voted directly into power and there would be a test of whether Eurocommunism plays by the democratic and Western rules. Frankly, given all the stresses on the European countries, it is just as well none of the communist parties forced such a test. This is not a suggest a lack of confidence in Europe. It is merely to say that the non-communist parties have been given a certain respite in coping with their countries' massive troubles.