A major new schism in the international communist movement was averted today when the Soviet Union agreed to turn a conference of pro-Kremlin parties here into a platform to launch a broad-gauged peace offensive instead of a rally of the faithful.

Fear that the conference, cosponsored by the French and Polish Communist parties, was an attempt by Moscow to reassert tight control over the participating party organizations led the important independent-minded Romanian, Yugoslav, Italian and Spanish Communist parties to stage a boycott. A scattering of minor parties, like the British and Icelanders, also stayed away.

Apparently sensing that resent U.S. foreign policy fumbles give them opportunities to widen their influence in Europe, the Soviets accepted the conciliatory efforts by the Polish and Finish communists rather than the hardline urgings of the French party to go forward just with the disciplined hard core of the movement.

In a formal appeal "to the peoples of the countries of Europe" for "peace and disarmament," the 22 participating parties called upon "communists, socialists, social democrats, Christians and believers of other faiths" to join in efforts to pressure the European members of the Atlantic Alliance to reverse their decision to allow the stationing of medium-range U.S. Pershing II and cruise missiles that can hit the Soviet Union from Western Europe.

The communist parties called for the convening of a special conference in Warsaw of European governments "for military detente and disarmament on our continent."

Polish delegates said in the corridors that this could include the United States and Canada and all the other countries that took part in the Helsinki conference on European security. The Poles said there have already been preliminary diplomatic contacts with Americans, but they did not explain in detail how such a meeting would differ from the conference scheduled for Madrid in November as a follow-up to the Helsinki meeting.

The Finnish Communist also got general support for their call for another Helsinki conference of "popular forces" including socialist and Christian Democratic parties.

This approach left the door open for the absent communist parties. From the podium of the two-day closed-door conference at the Hotel Meridien, "Nobody said a bad word about anyone who was absent," one of the Poles noted.The need for an appeal to the socialist parties was, in fact, an idea first advanced by Romania to justify its decision to stay away from Paris.

The moderate line finally adopted here was a sharp contrast with the last conference of European communist parties in 1976 in East Berlin, where attacks on the Chinese Communist leaders were one of the main features. w

The Paris conference was the first of its kind to bring together European ruling and non-ruling parties in a Western setting.

There were still strong traces of the hard line in the text of the speech by Soviet delegation chief Boris Ponomarev, who said, "There is no third way" between the Atlantic Alliance and the Soviet-led Warsaw Pact nations.

While there was no trace of the earlier Soviet stress on choosing sides between East and West in the conference's final appeal, there were clear references to Ponomarev's attacks on the United States as a danger to Europe.

Referring to the abortive U.S. military rescue mission in Iran, Ponomarev said, "Recent days have shown with sufficient eloquence the inconsistent and unpredictable behavior of the U.S. administration, its tendency to go to extremes, to become hysterical, to act unexpectedly without consulting with anyone at all."

None of the socialist parties of the major West European countries seems likely to attend a communist-backed Helsinki conference on such themes, yet there are influential leftist factions in all of the parties that could be tempted to join a campaign against U.S. missiles.

In addition to Scandinavian socialists, the parties the most vulnerable to such an appeal may be in Belgium and the Netherlands. Those two countries have accepted with reservations the stationing of U.S. medium-range missiles to counteract the Soviet SS-20s targeted on Western Europe. They are regarded as the most prone to accept Soviet pressure to reverse themselves.

If they did so, it could start an unraveling process in the Atlantic Alliance that would have unpredictable consequences, perhaps first of all in West Germany. Chancellor Helmut Schmidt headed off objections from the left of his ruling West German socialist party by insisting that Bonn not be the only continental capital to accept the U.S. missiles. A Belgian and Dutch defection would leave West Germany isolated with Italy as continental recipients of the U.S. weapons.

Soviet propagandists are already using U.S. failure to consult its allies on the sortie into Iran as an argument against the stationing of American rockets in Europe.

As the Soviet party newspaper Pravada, put it, "After all this, can certain-people in the NATO countries still hope that the White Houe would consult them when it contemplated the use of missiles deployed on their territory?"

The Soviets evidently think that it is quite possible to turn the propoganda tables on the United States, replacing the impression of the Soviet Union as an aggressive power in Afghanistan with one of the United States as the aggressor in Europe.

On the day of the Iran raid, French Foreign Minister Jean Francois-Poncet had been planning to give a ratio-television interview about what French officials are calling "the Siberian chill" between them and Soviet Foreign Minister Andrei Gromyko during his visit here last week. But, the minister's aides said, "He decided to let it drop because he knows very well that nobody would ask him much about Afghanistan. He would have been primarily questioned about Iran. Under the circumstances, he decided that the most charitable thing he could do was to keep quiet."