President Reagan denounced the Soviet Union yesterday in terms reminiscent of the chilliest days of the Cold War but spoke gently of Iran, seemingly opening the door to reconciliation with the nation that held 52 Americans captive until Reagan's inauguration.

He appeared to rule out any act of revenge against Iran for holding the captives for 444 days and indicated the United States might be willing to give aid to Iran in the future.

"Well, what good would just revenge do and what form would it take? I don't think revenge is worthy of us," Reagan said. He also indicated he will honor the commitments former president Carter made to Iran in return for the hostages' release.

Reagan established a tone for U.S.-Soviet relations far different from that of his Republican and Democratic predecessors of the 1960s and 1970s at his first presidential press conference by labeling detente a one-way street and accusing Moscow of condoning lying and cheating in order to achieve its goals.

The president said the Soviet leaders still aim at a world revolution to create a worldwide socialist or communist state.

At the same time that Reagan fired his rhetorical salvos at Moscow and claimed that Soviet leader Leonid I. Brezhnev, like all his predecessors, has repeatedly publicly embraced the goal of a one-world state, the president did not rule out arms negotiations and business deals with the Soviet Union in the pattern that has become familiar since former president Nixon launched detente.

Reagan said he was willing to enter "discussions leading to negotiations" on strategic arms reductions and indicated that he may follow through on his campaign pledge to lift the grain embargo against Moscow, imposed by Carter after Soviet troops invaded Afghanistan. But he said discussions in any one field would be affected by Soviet actions in all others. "In other words, I believe in linkage," he said, referring to a concept that the Carter administration deliberately abandoned.

"I know of no leader of the Soviet Union since the revolution and including the present leadership that has not more than once repeated in the various communist congresses they hold their determination that their goal must be promotion of world revolution and a one-world socialist or communist state, whichever word you want to use," Reagan said.

"Now, as long as they do that and as long as they at the same time have openly and publicly declared that the only morality they recognize is what will further their cause, meaning they reserve unto themselves the right to commit any crime, to lie, to cheat, in order to attain that, and that is moral, not immoral, and we operate on a different set of standards, I think when you do business with them, even as a detente, you keep that in mind," Reagan continued.

Soviet experts pointed out that the appeals for world revolution and a one-world communist state which were issued frequently through the era of Nikita Khrushchev disappeared from Soviet leaders' speeches in the mid-1960s.

On Iran, Reagan said that the lack of a stable government that could work its will in Tehran had been a major stumbling block during the hostage negotiations, but that if Iran managed to create a stable government, it might look for help from the United States.

"Now, I think that any country would want to help another if they really showed an intent to have a government that would abide by international law and do what they could to help them in that regard, but until such a thing appears apparent, I don't know that there's anything we can do," he said.

Reagan said the administration is still reviewing all the terms of the agreement that brought the hostages home, and considering its options on policy toward Iran, and he said he would wait for that review to be completed before discussing details of his administration's Iran policy.

However, Reagan said, "I'm certainly not thinking of revenge" but he made his position a little less clear by also saying that the United States cannot act as though the hostage seizure never happened.

Reagan said he would not encourage American businesses to resume relations with Iran at this time, but his reservation seemed primarily based on fears for the safety of Americans there.

"My opinion of American companies that want to resume business with Iran? I hope they're going to do it by long distance. We wouldn't want to go back to having just a different cast of characters but the same show going on," the president said of the possibility the other Americans might be seized by Iranians.

Reagan's conciliatory attitude toward Iran was in marked contrast to the administration's early and ongoing effort to warn that terrorists who attack Americans in the future face what Reagan Tuesday called "swift retribution."

The president elaborated on this theme in his press conference.

"People have gone to bed in some of these countries that have done these things to us in the past confident that they can go to sleep, wake up in the morning and the United States wouldn't have taken any action. What I meant [by "swift retribution"] was that anyone who does these things -- violates our rights in the future -- is not going to be able to go to bed with that confidence."

He said it would be inappropriate to discuss what actions he would be willing to take against terrorists. "This is a big and it's a powerful nation. It has a lot of options open to it, and to try and specify now just particularly what you should do I think is one of the things that's been wrong" in the past, Reagan said.

Terrorism also was under discussion at the State Department yesterday and the focus of the administration's attack was the Soviet Union. Spokesman William Dyess clairfied what Secretary of State Alexander M. Haig Jr. meant at his Wednesday press conference when he accused the Soviets of supporting and expanding international terrorism.

Haig was thinking of financial support, training and arms aid to the Palestine Liberation Organization and the use of surrogates "such as Cuba and Libya as conduits for assistance of all kinds to groups which advocate and use the tactics of terrorism," the spokesman said.

The secretary also had in mind Soviet broadcasts to Iran that tried to justify the taking of hostages, Dyess said, as well as "the general Soviet advocacy of armed struggle as the solution to regional problems from El Salvador to Namibia."

Reagan hailed the election of Jamaican Prime Minister Edward Seaga, who on Wednesday became the first foreign leader received by Reagan at the White House, as the signal of "a great reverse in the Caribbean." Reagan said "it was the turnover, turn-around, of a nation that had gone certainly in the direction of the communist movement." Reagan called former prime minister Michael Manley "a protege" of Cuban President Fidel Castro.

Reagan said "Mediterranean" when he meant to say "Caribbean" as he described his belief that Seaga's election provides an opportunity "for us to have a policy in the [Caribbean] of bringing them back in -- those countries that might have started in that [communist] direction -- or keeping them in the western world, in the free world."