President Reagan said today that allied leaders had agreed to "act together" to fight terrorism in a way that does not preclude unilateral military action such as the U.S. bombing attack against Libya.

But Reagan also said the leaders had agreed that the battle against terrorism "shouldn't be dependent on a single nation to try and find an answer" to terrorism.

In a news conference at the conclusion of the seven-nation economic summit, Reagan said the leaders are ready to "isolate those states that provide support for terrorism, to isolate them and make them pariahs on the world scene and even, if possible, to isolate them from their own people."

Reagan denied that the U.S. bombing of Libyan targets was intended to kill Libya's leader, Col. Muammar Qaddafi. But he added, "I don't think any of us would have shed tears if that had happened." Responding to a question about news reports of plans for a possible renewed U.S. attack against Libya, Reagan said none was planned.

Although the April 15 U.S. military strike was criticized by some allies at the time, Reagan stressed repeatedly today that the leaders had agreed to a "unified front" in opposing terrorism.

While the United States reserves the right to act unilaterally, Reagan suggested that the allied leaders would decide jointly on future retaliation against terrorists. He said the nations "together will decide upon what is appropriate, depending on the acts, what is the most effective thing to do . . . "

Reagan said the leaders had discussed all the "tools and weapons" available for combatting terrorism, although the allied leaders have offered differing views on how far they are willing to go. Reagan acknowledged that the other leaders had privately discussed with him their nations' economic and political ties to Libya. "All of them were talking about their problems, their relationship with Libya, and many of them were making suggestions as to what they thought they were going to do."

The president, in response to a question, confirmed that the administration had told U.S. firms with interests in Libya "to dispose of their holdings by June 30." Five U.S. oil companies were allowed to continue operations in Libya after the January implementation of the U.S. trade embargo against Libya.

The president said the Tokyo statement on terrorism, issued Monday, was a message to nations besides Libya that also sponsor terrorist actions. The leaders are "saying to those other countries,'We intend this to make them think also and realize that they are covered by this agreement -- that they will have to face all of us united if we get evidence that they are doing this.' "

Reagan's comments came at the end of what he described as "this triumph at Tokyo," saying it was the most successful of the six summits -- convening the leaders of the seven major industrialized democracies -- that he has attended as president.

"We arrived at this summit as a rising tide of prosperity . . . and together we committed ourselves in Tokyo to strengthen those [free-market] policies when we return home," he said.

Commenting on another topic that dominated the summit, Reagan, in his opening statement, criticized Soviet handling of information about the nuclear accident at Chernobyl on April 26. "A breakdown at a nuclear power plant that sends radioactive material across national frontiers is not simply an internal problem," he said.

But in response to a question, Reagan said, "I am pleased to say that in the last few days there has been a change, and the Soviet Union has been more forthcoming about this with regard to getting information and so forth."

Asked about administration policy on future adherence to the unratified SALT II arms control agreement, Reagan acknowledged that the administration was considering dismantling two Poseidon submarines later this year, a step that would be needed to stay within the treaty's limits on nuclear weapons when a new Trident missile-carrying submarine goes into service.

But the president insisted that a decision to dismantle those older subs would not be made to comply with the treaty, but rather because it was best "economically."

This is a formulation devised in the Pentagon by officials who have urged Reagan to abandon his policy of not undercutting the treaty, which he termed "fatally flawed" in the 1980 presidential campaign but subsequently has pledged to respect if the Soviets did likewise. A decision to dismantle the subs would represent a continuation of that policy, regardless of the words used to describe it.

Reagan predicted that the Tokyo statement on terrorism would have more impact than the 1984 statement in London, which was followed by continued terrorist attacks.

"I think there is reason to believe that, because we have all seen the evidence and we've all seen the fact that the victims of the terrorist attacks and the place where the attacks take place are such that almost any incident is -- involves more than one country to begin with," he said.

The president claimed that through intelligence-sharing, other nations had aborted 126 planned terrorist attacks and that U.S. intelligence had discovered 35 planned attacks. Reagan congratulated French President Francois Mitterrand for successfuly uncovering and preventing a planned attack on Americans lined up to get visas at a U.S. office in Paris.

Reagan said one of the "wonderful things that came out of this summit" was discussion with Mitterrand on France's refusal to allow American warplanes to fly over its territory on the way to Libya. While there may be differences among allies, he said, "I don't see a divorce in the offing."