The official Soviet news agency Tass gave a detailed explanation today of why it had censored some books and magazines from a U.S. photography exhibit, although it praised the show overall.

Tass gave these examples to show the reasoning behind the government's ban on 25 titles of the 350 books and magazines that Americans sought to include in the show:

Two publications were barred because they "contain photos bordering on pornography"; the book "Alaska" was banned because it "contains an allegation about the Soviet Union's military menace to the United States"; and Alastair Cooke's book "America" was forbidden "because on pages 312, 356 and 381 [it] proclaims that the Soviet Union 'seized' Eastern Europe and that West Berlin is in the line of the front against the Communist world and so on."

The Tass explanation was a response to published charges last week by Philippe Duchateau, administrator of the exhibit "Photography USA," that censorship of the show has been unusually severe. Duchateau has worked on several U.S. exhibits here. The photo show opened in Moscow last week, the final city of a six-city tour of the country that began last summer.

The American embassy had no official comment on either Duchateau's remarks or the Tass retort. One informed Western diplomatic source called it "interesting" that Tass praised the show. The news agency called the exhibit "a success from the very start" and had kind words for Frank Ursino, the embassy's exhibit director.

But Tass attacked Duchateau, saying his complaints performed "an anti-Soviet role that is now fashionable among certain circles in the West."

"It is clear to all for what kind of cultural exchange Phillipe Duchateau pines, forgetting that he is staying in a country whose laws and hospitality he should respect." Tass said.

The frankness with which Tass discussed its government's intrevention in the materials of the show provides a glimpse at the attitudes of a government that closely controls its media and carefully watches public expressions of all kinds.

Under Soviet rules, U.S. exhibit materials must be submitted two months in advance for review and approval. It was understood today that when Soviet reviewers balked at including the book "America" and some of the other materials, a U.S. official warned that it would be viewed as censorship.

"Of course it isn't," one Soviet official was quoted as replying. "This is just to inform you that If the materials are submitted then they will be censored."

News services reported the following developments from Moscow:

The government newspaper Izvestia sharply criticized American journalism in connection with the coverage of the Son of Sam murders. It outlined various news storeis, TV film plans and book contracts following the arrest of David Berkowitz and said: "Blood and money in this society of free enterprise will always be related to one another."

Soviet authorities arrested three more human-rights activists, bringing to 12 the members of the Helsinki monitoring group and its supporters seized this year.

The arrests of Felix Serebrov in Moscow and Viktoras Pyatkus and Antonas Tyerlaytskas in Vilnius, the capital of Soviet Lithuania, were reported by Pyotr Grigorenko, a former Soviet army general who is now a leading dissident.

Serebrov, 47, is a leader of the working group against abuses in psychiatry for political purposes.

The weekly Literary Gazette denounced prominent Jewish scientist Veniamin Levich for ingratitude, plargiarism, incompetence and defamation of his homeland. Levich, 60, an internationally known electrochemist, has been fighting for the past five years for permission to emigrate to Israel.

Tass reported that the Soviet Foreign Ministry complained to the American embassy about the failure to grant visas to four Soviet trade union representatives who were to have visited the United Sates earlier this month at the invitation of the National Committee for Trade Union Action and Democracy.

The Soviets charged that this contradicts bilateral agreements as well as the 1975 Helsinki agreement. An embassy spokesman said the matter is still under consideration in Washington.