A chorus of international protest erupted yesterday in Western Europe and the United States following Tuesday's conviction in Prague of six human-rights activists on charges of subversion.

Western European Communist parties, led by the influential and orthodox French, joined in condemning the Czechosolovak court's verdict while governments and international organization labeled it another serious violation of the Helsinki human rights accords. France's foreign minister postponed a visit to Prague in protest.

In Washington, State Department spokesman Hodding Carter called the convictions "a matter of serious concern."

L"Humanite, the official newspaper of the French Commmnist Party, headlined its page-one story on the trial "Iniquitous Verdict in Prague" and called for the release of the dissidents, five of whom received prison sentences of up to five years. The sixth defendant received a suspended sentence.

A spokesman for French Foreign Minister Jean-Francois Poncet said his visit to Czechoslovakia was postponed after a Cabinet discussion yesterday.

"France considers it [the court decision] contrary to the disposition of the 1975 Helsinki agreements and the spirit of detente that persons, or a group of persons, should be tried and sentenced for having sought the implementation in their country of the Helsinki agreements," which pledged the 35 signatory nations to facilitate freer movement of peoples and ideas.

Britain spoke of a concerted European action against Prague.

At least one Soviet voice also was raised in protest. Soviet dissident Andrei Sakharov, a Nobel laureate in physics, issued a statement in Moscow to Western reporters, saying the Czechoslovak activists were "unjustly persecuted" and appealing for a reduction in their prison sentence.

In a gesture of potentially great impact in overwhelmingly Catholic Czechoslovakia, Vatican Radio said the verdicts showed lack of recognition of and disrespect to "the dignity, the greatness of men, of the individual."

All six defendants had rejected prosecution charges that they were hostile to the state and the ruling Communist Party when they set up a committee to examine cases of alleged injustice and official abuse of power.

The two-day trail, from which journalists and supporters of the defendants were barred, sentenced prominent playwright Vaclav Havel, 43, to 4 1/2 years' imprisonment; economist Peter Uhl, 38 to five years; Vaclav Benda, 33, a former spokesman for the Charter 77 human rights movement, to four years; former television commentator Jiri Dienstbier, 42, and Otta Bednarova, 54, a journalist, to three years and Dana Nemcova, a Catholic and mother of seven children, to a two-year suspended sentence.

The proceedings conclude what is thought to have been the country's biggest political trail in seven years. Police took up positions in the streets outside the courthouse before the verdict was announced and both Western journalists and dissident supporters had been subject to obvious plainclothes survelliance.

The trail had been the subject of widespread Western protest even before the verdict was announced.

The lengthy official indictment charged the defendants with illegally publicizing alleged injustices by Czechoslovak authorities.It contained a new element that Western analysts said expanded the scope of the Prague government's continued suppression of dissent. It apparently signified that Czechoslovak citizens whose protests are publicized in the West apparently can now be prosecuted for subversive associations, even without having had personal contact with "hostile forces" outside the country.

In Moscow, the official news agency Tass published without comment a report on the trial yesterday while the Czechoslovak Communist Party daily Rude Pravo called the convictions just punishment for "undermining" the country's international prestige. "[The defendants] aims were no less than to threaten the political interests of our republic in the sphere of international relations." it said.

Communist parties outside Eastern Europe, where the trail was almost ignored, joined their French colleagues in sharp criticism. The Italian party paper, L'Unita, in a front-page story called it "a serious and inadmissible sentence." Spanish Communists called the trial a violation of human rights and liberties and the West German Communist Party called for the release and rehabilitation of the six.

J. F. Wolff, a Communist member in the Dutch parliament, echoed the criticism, branding the verdict "absurd and unacceptable."

In London, the British Foregin Office said Britain and its Common Market partners were considering action against Czechoslovakia. Irish Foreign Minister Michael O'Kennedy, on behalf of the EEC, denounced the verdicts.

A bipartisan motion filed by 68 British members of the House of Commons decried "the indifference of the Czech government to its obligations under Article 14 on the U.N. Covenant on civil and political rights." The liberal Guardian newspaper criticized the British government for receiving Czechoslovakia's fuels and power minister at the same time it officially condemned the trail.

The West German government said it regretted the verdict, pointing out that the jailings were out of tune with the political atmosphere in Europe since the 1975 Helsinki Security Conference.

In Prague, AFP reported yesterday that Havel, Dienstbier, Bednarova and Uhl have lodged appeals against their sentence. The news agency also said there was a chance of an appeal of all six sentences by the state prosecutor, since the court imposed shorter jail terms than he requested.

Organizations representing a wide range of interests in Western Europe added to the protests at the trail and sentences.

Amnesty International, The London-based human-right group, said it has adopted the six dissidents as "prisoners of conscience."

Amnesty had been singled out in the indictment of the six, as one of the "hostile forces" they had been in contact with abroad.