French President Francois Mitterrand said today that his country could not participate in the Reagan administration's Strategic Defense Initiative "in its present form," becoming the first major U.S. ally to reject a role in the project.

Mitterrand told a news conference at the close of the summit meeting of the seven major industrialized countries that he had given President Reagan his decision during an 80-minute private meeting between them Thursday.

More than any other allied leader, Mitterrand has expressed skepticism that the United States would ever share all research findings with its allies. He also has voiced deep concern that the U.S. research program into space-based defense could jeopardize the concept of nuclear deterrence.

Mitterrand said Reagan used the term "subcontractors" in referring to Europe's role in the SDI project, confirming his misgivings that France and other European countries would not be treated as equal partners with the United States.

"Subcontractors. That's the word I heard. The word was said in English. It confirmed my intuitions," Mitterrand said.

"The technology interests me, but the strategic project is interesting only for the future when man becomes master of space," he said. "I told Reagan France would not participate."

France has proposed a European research program, dubbed Eureka, that would explore civilian uses of outer space and other advanced technology involving fields such as lasers and high-speed computers. It would overlap with the SDI project in the French conception.

Mitterrand urged the other European countries to rally behind the "Eureka" project because of the "need to preserve their fund of intelligence, technology and brains. All this has to be mobilized in a great project that is European."

Mitterrand's announcement is expected to intensify the dilemma of West Germany and other allies, who may be forced to choose between accepting a subservient role in the U.S.-funded SDI project or sharing the costs with France in developing an alternative European research program.

West German Chancellor Helmut Kohl has called the SDI research project justified because the Soviet Union has been engaged in space defense efforts of its own. The Bonn government has indicated it may participate in SDI research if it gains adequate assurances that the United States will share all research findings and the benefits of related technology.

Senior West German officials said today that a team of government and industry specialists will travel to Washington in the coming weeks to discuss prospective SDI contracts for West German firms.

But Kohl also has kept open the possibility of participating in the French initiative either as an alternative or as an adjunct to a role in the SDI program. Mitterrand said today that "West Germany has given me full agreement for Eureka."

Britain's Prime Minister Margaret Thatcher has chosen to join the SDI research program and voiced some disdain for the French project, which British officials regard as too expensive and bureaucratic.

"I would be quite happy . . . to be directly involved with the Americans," Thatcher said. "I don't like the idea of there being anything confrontational" between Eureka and SDI.

Thatcher's spokesman said today that Britain had asked Washington for a chance to join the U.S. research program even before receiving a formal invitation.

Italy and the Netherlands also have shown some interest in the Eureka research project as a way to strengthen European unity and enhance the European Community's ability to compete with the United States and Japan in new technologies.

But the high cost of the Eureka program has frightened away most European governments, who have been pushed by private industry not to miss out on the chance for lucrative SDI contracts funded by Washington.

Japan and Canada have adopted a more cautious stance, saying they wish to learn more about the exact nature of the five-year, $26 billion research project.

U.S. officials said that Reagan received a variety of responses when he conducted bilateral talks with other leaders at the summit about their countries' possible contributions to space defense research.

"The offer to take part in the research program has been greeted in different ways by different countries," Secretary of State George P. Shultz said today. He said those leaders who expressed interest were intrigued by SDI's potential of opening up new technologies.

"The history of these things is that they are generally spin-offs of one kind or another," Shultz said. "Take the space program. It has spun a whole industry almost that comes out of miniaturization."

In rebuffing a role in SDI, Mitterrand suggested that the U.S. and French projects "could be bridged" once the specific outlines of the two research programs are known.

"They are certainly not incompatible," Mitterrand said. "We can have exchanges with the United States."

The French leader said the Eureka program has identified six areas of civilian research including lasers, optics and high-speed computers. The French research effort could eventually serve military purposes but its primary purpose would be "to explore space through advanced research in order to master new technologies," he said.

Mitterrand reportedly told Reagan that France is highly interested in the technology but not the strategic aspect of the U.S. program because it could alter the concept of mutual assured destruction that has maintained peace in Europe for 40 years.

The French revelation came as a startling development in an economic summit that earlier had avoided discussion of the controversial space defense research plan. Before the leaders gathered in Bonn, differences of opinion over the SDI project loomed as a vexing conflict dividing the United States and its European allies that threatened to dominate the summit.

The U.S. and West German governments, seeking to avoid a potential political confrontation, had previously abandoned the idea of making a joint SDI declaration when it became apparent that no consensus could be achieved among the seven participating leaders.

Kohl did not wish to dilute the summit's emphasis on the theme of peace and reconciliation 40 years after World War II by including SDI in the communique, West German officials said.

The Reagan administration also wanted to defuse a possible clash over SDI with its allies, particularly in the midst of a continuing political furor over Reagan's plans to lay a wreath Sunday at the Bitburg military cemetery where 49 Nazi SS troopers are buried, along with 2,000 other German soldiers.

In the end, any mention of SDI was dropped from both the political declaration and the final communique. Before reading the closing statement, Kohl alluded to the bilateral meetings that most leaders held with Reagan, and said they "warmly welcomed" the president's explanation that SDI "was not an attempt to attain superiority but rather to enhance strategic stability."

Kohl's comments, which were cleared in advance with the Reagan administration, pleased U.S. officials, who said they received as much support as they could expect, given the disparate views of the allies toward space-based antimissile research.

"They said that this would be the SDI summit," a senior U.S. official said. "The subject hardly came up, except in bilateral sessions." But he quickly added that the Reagan administration was not interpreting the muted talk about SDI as a blanket endorsement by the allies.