French President Francois Mitterrand's intransigence at the western economic summit is likely to win him political points at home during the period before crucial legislative elections next year.

The Socialist president flew back to Paris tonight at odds with other western leaders, including his principal European partners, on a calendar for global trade negotiations and participation in the research phase of President Reagan's Strategic Defense Initiative. His refusal to agree to a precise date for the opening of the talks blocked one of the Reagan administration's key goals at the summit.

Mitterrand's tough stand on the trade talks irritated other summit participants anxious to find ways of countering protectionist pressures in the United States and elsewhere. But it was described by French journalists covering the seven-nation summit as a political coup in the tradition of the late Gen. Charles de Gaulle.

"Isolation doesn't matter to a French president as long as he is isolated in his grandeur," said one French commentator, predicting that it would prove very difficult for the right-wing opposition to criticize Mitterrand for his performance in Bonn.

By vetoing a date for the new trade talks, according to this analysis, Mitterrand was projecting himself as the defender of the interests of French farmers who derive enormous benefit from the European Community's costly system of agricultural price fixing. He also was demonstrating an old Gaullist reflex in opposing the wishes of a president of the United States.

At a press conference after the summit, Mitterrand gave the impression of being unrepentant and even pleased with himself for managing to make France the pivot around which the meeting revolved. Shrugging aside suggestions that France was isolated from its major allies, he said: "To be alone in Bonn doesn't mean to be alone in the world."

Mitterrand's evident desire to win approval from French and world public opinion reflected the sharp change in the character of summits since western leaders held their first such meeting in a chateau near Paris in 1975. Originally conceived as an informal exchange of views on economic problems, the summits now have developed into annual political spectacles attracting intensive media coverage.

The Bonn summit, the 11th in the series, generated a larger number of issues than ever before -- ranging from monetary reform and "Star Wars" to Nicaragua and the 40th anniversary of the end of World War II in Europe.

While Mitterrand insisted that he was defending deeply held principles in refusing to agree to new trade negotiations, other summit participants were virtually unanimous in attributing his stubborness at least in part to domestic political considerations. They pointed out that Mitterrand's Socialist Party faced a strong challenge from the right in parliamentary elections a year from now.

Secretary of State George P. Shultz specifically cited the "French political scene" as an explanation for Mitterrand's intransigence. Another U.S. official speculated that global talks about agricultural subsidies in early 1986 could have provided ammunition to right-wing political parties in France in the middle of an election campaign.

A senior adviser to West German Chancellor Helmut Kohl who participated in most sessions commented: "The French have already entered an electoral phase; we have to expect this kind of behavior now."

For their part, French officials were caught off guard by the swiftness with which Kohl agreed to support the U.S. position on starting negotiations early next year under the auspices of the General Agreement on Tariffs and Trade (GATT). The German decision effectively destroyed French hopes of maintaining a united European front at Bonn.

By the end of the meeting, France was even abandoned by Italy, which previously had voiced mild opposition to a new GATT round. Mitterrand also was out on a limb as the only major West European leader to reject outright a U.S. invitation to take part in the research phase of Reagan's plan for a space-based antimissile defense system.

To add insult to injury, the French president's ideas on monetary reform were described as "generalized jabberwocky" by British Prime Minister Margaret Thatcher in a newspaper interview on the eve of the summit. A spokesman for Thatcher, who has been fiercely critical of European farm subsidies, said that Britain favored including discussion of agriculture in a new GATT round.

Before the summit began, French officials depicted the meeting as a test of Europe's "political will" to maintain its independence and cohesiveness in the face of pressure from the United States. As justification for his stand, Mitterrand cited a European Community declaration on March 19 that came out against setting a date for a new GATT round.