France informed the Soviet Union today that the future of detente depends on how fast and under what conditions Soviet forces are withdrawn from Afghanistan.

The warning came in a meeting here between Foreign Minister Jean Francois-Poncet and Soviet Deputy Foreign Minister G.M. Kornienko, who flew from Moscow to explain the Soviet position.

The Soviet visit by the man considered to be working chief of diplomacy under the aging Foreign Minister Andrei Gromyko underlines the importance that the Kremlin apparently attaches to the French postion, which has been the softest of the major Western allies.

Some French sources expressed surprise at the toughness of the French stand, relayed in a full day of meetings between Kornienko and top French diplomats.

Beyond a brief communique, however, the French Foreign Ministry spokesman refused to comment on the meetings failing even to characterize the tone of the discussions. Sources said the French side had decided that it can talk tough to the Soviets in private and hope to have some effect, provided that the strong language is not expressed in humiliating public declarations.

Franscois-Poncet told Kornienko that the Afghan intervention is "unacceptable" and "a serious threat to the achievements of detent," the communique said.

It referred to an "indication" by Kornienko that the Soviets are "ready to withdraw their forces from Afghanistan as soon as conditions permit." This recalled Soviet President Leonid Brezhnev's statement by hot line to President Carter that the troops would be pulled out as soon as they finished their job.

The French communique said that Francois-Poncet had "stressed that it is the schedule and the conditions under which that intention is applied that will be the decisive element to judge whether it is possible to restore in Afghanistan a situation that is in conformity with the rights of the Afghan people and with the demands of peace."

French sources said the Soviets were told that if there is no improvement in the situation, France could be forced to adopt the hard-line U.S. position perhaps going so far as joining the boycott of the Moscow Olympics. A French Cabinet statement yesterday said that the government had no intention to pressure the French Olympic Committee into reversing its decision to take part in the games.

Even though an opinion poll has indicated that two out of three French citizens oppose a boycott, the public mood seems to be shifting. The leader of the Christian Democratic-oriented section of the ruling party came out today for a boycott.

There have been a number of editiorials saying France would look foolish if it turned out to be the only major Western power to send athletes. Le Monde spoke of France's efforts to appease both the goat and the cabbage it is about to eat.

A petition favoring the boycott was signed this week by philosopher Jean-Paul Sartre and actors Yves Montand and Simone Signoret, generally viewed as sympathetic to the Soviets.

French Sports Minister Jean-Pierre Soisson reportedly is saying privately that he favored joining the boycott but that President Valery Giscard d'estaing ruled against his view.

The Soviet deputy minister arrived from Moscow last night on the same plane as French National Assembly President Jacques Chaban-delmas, the first important noncommunist politician from the West to visit Moscow since the invasion of Afghanistan. Chaban-Delmas cut short his trip by a week after news came of the arrest of dissident physicist Andrei Sakharov by Soviet authorities.