Soviet efforts to influence public opinion, especially in the Third World and western Europe, through "disinformation" tactics such as forged documents, front groups and media manipulation, have intensified and grown "somewhat bolder" in the past year, the State Department charged yesterday.

A new report by the department, updating one issued in July, 1982, lists several examples of "active measures" of deception that have been exposed in the past 14 months and that State claims were masterminded by the Soviet KGB or its sister services in Soviet-bloc countries.

The Soviets' main objective, the report said, continues to be to undercut the decision by the NATO alliance to install new missiles in western Europe late this year to counter Soviet missiles already in eastern Europe.

But an official, briefing reporters on grounds that he not be identified, also said "it would not be surprising" for the Soviets to attempt some disinformation tactics in connection with the search now under way in the Sea of Japan for the wreckage of the South Korean airliner shot down two weeks ago by the Soviets.

The official said Moscow might try to fabricate some documents or a flight plan that it could claim was aboard the plane to support Soviet charges that the Boeing 747 was on a spy mission. He said attempts to produce a phony "black box" in-flight recorder probably would be "difficult."

The new report cites the following:

* The publication in July by a "left-wing news weekly" in Italy of two forged cables supposedly from the U.S. Embassy in Rome that were intended to show that the United States had orchestrated the effort to implicate the Bulgarian secret service in the plot to assassinate Pope John Paul II.

* A forged document allegedly from the U.S. Embassy in Nigeria that was published by two opposition party newspapers in that country and linked the U.S. ambassador to a plan to assassinate two prominent Nigerian politicians.

The use of a forged West German document by the government of Ghana to back up accusations that the United States was planning an overthrow of the government in that country.

* A fabricated speech supposedly delivered by U.S. Ambassador to the United Nations Jeane J. Kirkpatrick that contained a false representation of U.S. policy and was published by a pro-communist Indian newspaper in New Delhi.

* Continued use of the World Peace Assembly as "the major communist front organization" to undercut U.S. efforts to install new missiles in western Europe.

* The expulsion of Soviet officials from Norway and Switzerland for interference in internal affairs involving attempts to gain influence with the peace movement and with media manipulation.

* The publication in February by a news weekly in Madrid of a phony 1978 memorandum on Poland from former Carter administration national security adviser Zbigniew Brzezinski suggesting that the United States was behind the troubles in Poland.

These episodes, and others in the report alleging such things as future U.S. deployment of cruise missiles in Africa, have been reported previously. But they are pulled together every year or so by the State Department in an effort to improve "recognition that the Soviets use these deceptive activities as standard tools," the official said.

The official said that although such activities did not endanger the United States, they do have an impact in the Third World and that "it is very hard to counter" such allegations because "the denials never really catch up" with the phony stories or front activities.

He said that the government in Ghana, for example, eventually accepted the U.S. explanation that the story and documents about an overthrow were false but that the incident still doesn't help relations.

In response to questions, the official said the United States does not engage in such activities and that "we couldn't get away with it" in an open society "even if we wanted to."

The report said that although at times it is difficult to be sure if it is the KGB or another Soviet-bloc disinformation bureau that is behind a specific incident, "the distinction is hardly significant given the close collaboration between the KGB and its sister services."