ust a week before President Francois Mitterrand is to open the industrialized world economic summit conference, he said today that "rarely have allied powers been so indifferent to each other's fate." He warned the consequences could be "economic war" among the seven participants.

Speaking to American correspondents at the Elysee Palace, Mitterrand nonetheless said that "on the whole" he was "not pessimistic" because the summit participants were "men of good will" even "if they did not work much together."

Looking fit and relaxed despite grueling foreign travel--he has just returned from a week in Africa--Mitterrand said that although he was hosting the three-day summit at Versailles starting next Friday, the proceedings were "not my conference."

Of his fellow heads of state he said, "Although we have different policies, we should be able to find things in common."

"We have coordination on arms matters," he said, "so why not on industrial matters? We must find a minimum of consensus," he added, indicating that the summit could well "start cleaning up the monetary system and pool technological resources."

Mitterrand singled out none of his fellow leaders--representing the United States, Britain, Canada, West Germany, Italy and Japan--but he did indirectly criticize President Reagan's economic policies.

"It's important to fight inflation," he said, "but if the fight against inflation amounts to lethargy, what does that mean? Remember that when you are dead you cannot catch cold."

France has been in the forefront of countries arguing that Reaganomics stifles recovery from the current recession, which has undercut French efforts to spend their way to increased growth.

Mitterrand, who has conferred with Reagan four times in the past year, said he felt the American leader was "a little bit more open." Reagan, he said, "has good will in the sense that he would like to see U.S. high interest rates lower but he believes, in the law of the market place, he cannot do anything about it."

Mitterrand plugged his "audacious new idea" for technological cooperation, which he will present to the three-day summit conference opening Friday.

"If we all work on the same range of products," he said, "we will all be obliged to protect ourselves," apparently meaning that such cooperation could deal with emerging protectionism.

Mitterrand acknowledged that such a major venture--what he called the "third industrial revolution"--required government planning and that "many countries hate" such an approach.

Although the president said "I do not wish the franc to be submitted to the will of others," he acknowledged the growing pressures on the currency might prompt France to leave the European Community's monetary system.

France in recent months has spent billions of dollars to defend the franc, which Mitterrand described as "in the front lines" since the Belgian franc was devalued in the winter. He did not answer a direct question about devaluing the franc but said, "I do not consider I will fall into Hell" if he took that action. "I do not rule out any hypothesis," he said.

Mitterrand said he felt the "architecture" of existing international institutions--apparently ranging from the Atlantic Alliance to the International Monetary Fund, the World Bank and the Organization for Economic Cooperation and Development--remained "very good."

But he said these institutions had been "emptied over the past ten years like a house in which people had taken away the furniture so that it was not easy to eat or sleep there." What was needed, he said, was "not to rebuild new architecture, but to restore the architecture we have."

Asked about American pressures to tighten up credit terms for the Soviets, Mitterrand said, "We do not want to suppress trade with the Russians, but we do not want to increase their resources either."

He said France had been "very helpful" in denying sales of strategic and sensitive products to the Soviet Bloc within the Paris-based Cocom organization which handles such matters." But the seriousness of East-West relations is not such as to justify a bellicose attitude," he added, as if to register reservations about the approach favored by some U.S. officials.