National security affairs adviser Richard V. Allen, labeling the Palestine Liberation Organization a terrorist group, said in an interview made available yesterday that the Israeli raids into Lebanon were justified as legitimate hot pursuit.

Allen, chief White House foreign affairs aide to President Reagan, also said the Soviet Union supports the "main aims" of the PLO -- the destruction of Israel -- and suggested there is possibly "minimal Soviet involvement in the PLO organization itself."

Past administrations, maneuvering for a peaceful accommodation in the Middle East, have refrained from publicly describing the PLO as a terrorist organization. Nor has there been any public statement that could be interpreted as American sanction for Israel's repeated air and seaborne strikes against guerrillas in Lebanon.

Allen's statements, to be broadcast by ABC-TV Thursday, could cloud Secretary of State Alexander M. Haig Jr.'s reception next week in Saudi Arabia, Egypt and Jordan, all of which support the PLO. But his welcome in Israel will likely be warm.

[In what White House press secretary James S. Brady called an effort to avoid speaking with "many voices," Allen yesterday canceled an off-the-record speech to a group of young Republicans in Washington when reporters refused to leave. Vice President Bush has addressed the group earlier.]

Asked in the ABC interview if it would be fair to call the PLO a terrorist organization, Allen replied: "I think yes, on balance. There's no question that we must identify the PLO as a terrorist organization -- until it provides convincing evidence to the contrary."

Allen also said that, "to my chagrin," terrorism has proven effective for the PLO, considering the legitimacy accorded the organization in the United Nations.

Reagan referred to the PLO as a terrorist organization during last fall's campaign, but U.S. policy on the issue has not officially changed. The State Department maintains that only some elements of the PLO are terrorist units.

Allen was asked whether the Israeli raids into Lebanon, most of them preemptive strikes, were acts of terrorism or self-defense.

"I don't want to get into a specific policy discussion here and what I'm saying does not represent the -- I emphasize the -- official policy of the United States government, but to the extent that one reaches to the source of terrorism then, of course, there is ample justification for taking action," Allen replied.

"I'm just saying that reaching to the source is generally recognized as hot pursuit of a sort and, therefore, justified," he said.