Four decades of fraud are enough. The coincidence of the historical calendar and the quickening pace of what is called U.S.-Soviet "dialogue" make this the moment for the United States to denounce the agreements entered into 40 years ago at Yalta.

These words open a chapter in the final volume of Churchill's history of the war: "As the weeks passed after Yalta it became clear that the Soviet government was doing nothing to carry out our agreements. . . ." Churchill was referring especially to Poland, on whose behalf Britain had gone to war in 1939, when the Soviet Union was Hitler's ally.

In February 1945 the Soviet Union began sealing Poland from Western eyes and destroying democratic elements. There were fewer of those elements than there might have been. When the Polish resistance rose in Warsaw against the Germans, the Soviet army loitered on the outskirts of the city to allow the Nazis to massacre the Polish freedom fighters, who would have been inconvenient for the arriving Soviet totalitarians. The Soviet Union compounded its crime by even refusing to allow U.S. and British planes to land in Soviet-held territory after dropping supplies to the Polish resistance. This was six months before Yalta.

The Yalta conference ended Feb. 11, 1945. On Feb. 27, Andrei Vyshinsky, the satanic prosecutor at the 1930s Moscow show "trials," arrived in Bucharest, Romania, to demand that King Michael dismiss the all-party government. The next day, Churchill wrote, Vyshinsky returned to the king, "banged his fist on the table, shouted for an immediate acquiescence, and walked out of the room, slamming the door. At the same time Soviet tanks and troops deployed in the streets of the capital, and on March 2 a Soviet-nominated administration took office."

The Yalta agreements "binding" the allies to work for open societies in Eastern Europe were, at best, forlorn attempts to blunt Soviet bayonets with parchment. It took six days for them to be revealed as an empty pretense.

Yalta did not "give" Eastern Europe to the Soviet Union. The Red Army took it. But Yalta codified the West's wishful thinking about the Soviet Union. The latest Shultz- Gromyko session, like the arms control process generally, is another manifestation of the hope that if the Soviet Union can be talked into talking, and into adopting the forms of orderly relations, then the substance of such relations will somehow follow.

Perhaps we should periodically enter into agreements like those signed at Yalta or, 30 years later, at Helsinki, if only for what they can teach. That is, such agreements can be useful because of the lesson that can be extracted from the instant and comprehensive Soviet violation of them. The problem is that Western governments wid up teaching their publics precisely the wrong lesson. They refuse to teach the lesson by denouncing the agreements. Instead they convince themselves and their publics that there is something inherently wholesome in the mere "process" of producing agreements.

It may be argued that denouncing the Yalta agreements would be an empty gesture. Not true. It would be an act of public pedagogy, underscoring a lesson at a pregnant moment.

Plans are now being made for commemorating the 40th anniversary of the end of the war in Europe, and there is a revival of the sort of sentimentalism that helped produce Yalta. Today the sentimentalism is, "We were friends then, so . . ." "Friends," forsooth. In 1945 the sentimentalism took the form of the belief that the Soviet regime (which can claim legitimacy only as the enemy of bourgeois democracies) would desire in peace a continuation of the cooperative relationship that served it well in war.

In 1985, the anniversary of V-E day will be an appropriate moment for commemorating the fact that the Soviet Union began the war as Hitler's enthusiastic ally. It was convinced that Hitler would destroy England and other decadent bourgeois democracies, and was eager for that outcome. Hitler initiated the rupture with the Soviet Union, which then received enough aid from the decadent bourgeois democracies that it could survive and become the legatee of Hitlerite values -- conquest, totalitarianism, anti-Semitism.

This June will mark the 10th anniversary of the Helsinki agreements on human rights. Those agreements are extensions of the Yalta agreements, but are even less defensible because they came after 30 years of experience with the Yalta agreements. Under the Helsinki agreements the Soviet Union undertook to stop being the Soviet Union -- that is, to be minimally civilized.

It has, of course, declined to do that. So 1985 is the year also to denounce the Helsinki agreements. A decade of fraud is enough.