President Reagan said yesterday he would use military force against Iran or Syria if presented with clear evidence that one of those governments had sponsored an act of terrorism against Americans.

"State-supported terrorism is a form of warfare, and you just can't sit by and let somebody else declare war on you and pretend that you're still at peace," Reagan told a group of columnists and commentators in the White House family theater when asked whether he was willing to use force against Iran or Syria if they sponsored terrorist incidents.

The president said that in many instances it was difficult to obtain the "irrefutable evidence" he said the United States had before its April 14 bombing raid on Libya. But he added that when such evidence exists, "we must have the same policy" in dealing with state-supported terrorism.

Reagan was then asked whether this meant using force against Damascus or Tehran. He replied, "Yes, if we had that kind of evidence."

The president's comments came an hour after he issued a sweeping call for political and economic freedom throughout the world in a speech to an international forum of the U.S. Chamber of Commerce.

He combined this message with a stern warning to Libyan leader Muammar Qaddafi that the United States is ready to strike again if Libya sponsors further acts of terrorism. Reagan and other U.S. officials have said that the April 14 attack was based on evidence of Libyan responsibility for the bombing of a West Berlin night club in which a U.S. soldier and a Turkish woman were killed and more than 200 persons injured.

"By nature, we prefer to solve problems peacefully," Reagan said. "But as we proved last week, no one can kill Americans and brag about it. No one. We bear the people of Libya no ill will, but if their government continues its campaign of terror against Americans, we will act again."

In his meeting with the columnists, Reagan said he had been "encouraged" by recent allied reactions to terrorism "in spite of the fact that they didn't come as far as we would like."

Citing the expulsions of Libyan diplomats and students by European nations and praising the sharing of intelligence information, Reagan said that "progress" was being made in allied cooperation.

Reagan's speech to the chamber previewed themes he intends to emphasize during a 12-day trip in which he will meet representatives of six Southeast Asian countries in Indonesia and leaders of six industrialized democracies at the 12th Economic Summit in Tokyo. The president said that when he leaves Washington on Friday, Air Force One will be propelled on its 23,000-mile trip by "the winds of freedom," a phrase he used eight times during his address.

Echoing the major theme of his speech to the U.N. General Assembly last October, Reagan said that democracy was on the march throughout the world. He also reaffirmed U.S. support for "freedom fighters" in Nicaragua, Angola, Afghanistan and Cambodia.

His audience listened attentively to Reagan's message that "freedom and economic advance go hand in hand" but interrupted with applause only when he said he was ready to repeat the raid on Libya if further incidents of terrorism are traced to Qaddafi.

For the first time, the president also appealed publicly to Arab nations to join the United States in opposing Qaddafi.

"Arab nations themselves have been forced to endure terrorist attacks from this minority," Reagan said. "We hope and pray the Arab world will join with us to eliminate this scourge on civilization."

The president said it was "hypocritical" for Qaddafi to expect "unquestioned support from the Islamic world" in view of his alliance with the Soviet Union.

"Nowhere is the slaughter of Moslem people greater than in Afghanistan," Reagan said. "Yet, Col. Qaddafi allies himself with those perpetrating this crime on Islam and all mankind."

In an interview with foreign journalists released yesterday by the White House, the president said he would sound out allies about a proposed $20 billion to $30 billion development plan for the Middle East, a region he called "the touchpoint that could set off world conflicts."

The idea was suggested on a recent visit to Washington by Israeli Prime Minister Shimon Peres, who called it a "Marshall Plan" based on the U.S. reconstruction effort in Europe after World War II. Reagan did not use this term in giving qualified support to the idea.

In the interview, Reagan downplayed differences with allies over the Libyan raid, saying that when the allies discuss terrorism "we probably will find, in Tokyo, that we all are in more agreement than some of the impressions that have been given."

Throughout the day the president outlined U.S. objectives at the Economic Summit, stressing commitment to open markets and fair trade and pointing out that the strong dollar, which had been "a legitimate concern" to European countries and Japan, was now declining. He also said he would not surrender to domestic demands for protectionism.

"Now is not the time to surrender to trade-killing protectionism," Reagan told the chamber. "The trade imbalance should be solved through multilateral negotiations that open markets, not unilateral legislation that closes them. The right answer is not decreasing imports, but increasing our exports."