French Foreign Minister Claude Cheysson said yesterday there can be no French cooperation with Libya until all its forces are withdrawn from Chad in keeping with the French-Libyan agreement of Sept. 17.

At a news conference following his meetings with Secretary of State George P. Shultz and other U.S. officials, Cheysson said France plans to pursue "contacts, negotiations" with Libyan leader Muammar Qaddafi despite a U.S. view that this is unwise.

Cheysson reported, "There is a difference of mind between the Americans and us" on dealings with Qaddafi, whom he referred to as "the responsible leader of Libya." But he said of the difference on this point with the United States, "We can live with it."

The U.S. position is that Qaddafi is untrustworthy, and that any contacts that build his stature are unhelpful. The State Department, however, continued to say little on the subject yesterday to avoid further complications for an already-embarrassed French government.

In a breakfast meeting with Washington Post editors and reporters, Cheysson said "the bulk" of Libyan troops have been withdrawn from Chad but that France has suffered "a real disappointment" because not all the Libyan forces have left as had been previously agreed.

"We demand that the withdrawal should be total as was agreed," Cheysson said.

The French foreign minister's discussions, which included meetings with Vice President Bush, Defense Secretary Caspar W. Weinberger and others in addition to Shultz, reportedly centered on such major subjects as East-West relations and arms control, with the contentious issue of Chad taking only a small part of the time.

Cheysson told his news conference that he pursued "questions" with the senior U.S. officials about military strategy and arms control, especially in view of the potentially major changes and complications that could be introduced by the Strategic Defense Initiative, popularly known as Star Wars, backed by President Reagan.

In explanation of the strange turn of events involving France, Libya and Chad, Cheysson maintained during his discussions at The Post that satellite photography had earlier shown that Libyan troops had "almost totally withdrawn" from Chad. He suggested that these U.S.-supplied photos backed up the Nov. 10 French announcement that withdrawal of both Libyan and French forces had been total and complete in keeping with their bilateral accord. Saying that some Libyan forces have inhabited a mountainous area, Cheysson said it had not been possible to be sure from the air if the pullout were "total."

It was "a real disappointment when we realized there had been a breach of the commitment and they Libya had sent back some people," Cheysson said. He did not give an estimate of the troops "sent back" but said that they were "lightly armed, with very limited equipment."

State Department spokesman John Hughes said it is considered possible by U.S. officials that some Libyan troops could have left and come back.

A senior U.S. official who asked not to be quoted by name said Washington believes "the bulk" of the Libyans never left. The official indicated that the current U.S. intelligence estimate is that close to 3,000 troops of Libya's original force of 5,500 troops remain in Chad. French officials say the number is closer to 1,000.

There was no indication that Cheysson's discussions here relieved U.S. apprehension about the situation in Chad and other aspects of Libyan policy under the leadership of Qaddafi.

However, both U.S. and French sources described the atmosphere of Cheysson's meetings as cordial. Shultz went out of his way to turn up at the French Embassy for cocktails Monday night to show he was not snubbing Cheysson, even though he did not attend a dinner there in honor of Cheysson. A U.S. spokesman portrayed this omission as normal.

The French-Libyan agreement, according to Cheysson, notes that "if one of the parties does not fulfill the commitment the other party would be relieved of its commitment." He went on to say, "We came because they had come. If they stay, we stay. If they withdraw, we withdraw. If they come back, we come back."