The Hungarian government today prohibited a group of western and dissident East European intellectuals from staging an independent public symposium as delegations from 35 nations gathered here to review cultural issues of the Helsinki Accord on East-West cooperation.

Executives of the International Helsinki Federation for Human Rights said the Hungarian foreign ministry told them this afternoon that they would not be allowed to hold the planned symposium on "Writers and Their Integrity" in a public meeting room of the Duna-Intercontinental Hotel here.

Instead, some 70 writers, intellectuals and human rights activists invited by the federation crammed into a private apartment tonight to carry on what they call a "free intellectual exchange." Participants included leading Hungarian and Czechoslovakian dissidents as well as such western representatives as American writer Susan Sontag, Israeli novelist Amos Oz, and German poet Hans Magnus Enzensberger.

"This is the first step of European intellectuals to meet each other and have a free discussion beyond all borders of the state," Hungarian writer George Konrad told the gathering. "We should have the right to hold this meeting in public, but if we don't have a public place every apartment will be public."

The two-day independent symposium was timed to coincide with the opening assembly of the Cultural Forum of the Conference on Security and Cooperation in Europe, better known as the Helsinki process. Participants are signatories to the 1975 Helsinki Accord on security, cultural and economic exchange and human rights.

The cultural forum is the fifth follow-up meeting to the Helsinki conference and the first to be held in the Soviet bloc. Official tolerance for the independent meeting was considered a key test for the Hungarian government and its communist-ruled allies, which have been accused of not living up to Helsinki provisions on censorship, free expression and other human rights.

The government's action today surprised Helsinki Federation organizers and drew a strong protest from U.S. officials who have been privately urging Hungary to allow the symposium.

A statement by Walter Stoessel, the chief of the U.S. delegation, said the ban was "a violation of Hungary's commitment" to "allow the full range of activities for nongovernmental organizations" in Budapest. "This has harmed the spirit of the Budapest cultural forum and is not conducive to the aims" of the Helsinki process, Stoessel's statement concluded.

Hungarian officials offered no public comment on the ban, which was communicated to organizers in a private meeting.

Helsinki Federation officials said they were surprised by the action, which came only hours before the first meeting of the symposium was to begin and after most participants had already arrived in Budapest. "We really thought we were going to come through without any problems," said Gerald Nagler, the executive director of the Vienna-based federation. "We were surprised when we found out today this was not the case."

Nagler said Hungarian officials justified their action by saying the federation had not asked for official permission to hold the gathering. He argued, however, that agreement at previous Helsinki meetings in Madrid and Ottawa confirmed the right of independent groups to stage meetings at such conferences.

"The Hungarian government was fully informed of our intention in advance," Nagler said. "We did this through many channels to avoid an overreaction. We did not see any signs of nervousness on their part. We assured them that we weren't terrorists."

Nagler said that the symposium would continue here "in a less organized way" through meetings in private apartments. "We will look for other solutions. We are not going home," he said.

Several Hungarian and western writers managed to deliver brief introductory statements tonight as the symposium group crowded with western reporters into the two-room apartment of a Hungarian poet here.

Sontag, the first American to speak, said that she had rejected an invitation to join the official U.S. delegation to the forum in order to participate in the independent meeting. "This is not because I think I am more free here," she said, "but rather because I want to support the principle that meetings that are not government-sponsored can and do take place. This is part of the meaning of the Helsinki process."

The official forum, attended by about 800 delegates, is expected to discuss a variety of cultural issues in committee meetings over a period of six weeks. Soviet bloc delegations have sought to focus the discussions on cultural exchanges and have suggested a final statement stressing the value of cultural cooperation between East and West, U.S. officials here said.

The officials said the United States would not agree to a final statement unless it included references to issues of free expression and uncensored dissemination of information. The Reagan administration has urged American cultural representatives participating in the forum to stress such human rights issues in committee meetings, officials said.

The U.S. delegation includes playwright Edward Albee, jazz musician Billy Taylor, architect Peter Blake and other private citizens from various cultural fields.