French President Francois Mitterrand, lowering his expectations and his tone, emerged from the Williamsburg summit a satisfied guest, in contrast to his role as disgruntled host of last year's divisive seven-nation conference at Versailles.

In an hour-long news conference today at the summit's conclusion, a low-key Mitterrand pronounced himself satisfied at obtaining what he wanted in the summit declaration--a mention, however vague, of his ideas on monetary reform and currency stability--and at having kept out of a declaration on arms control what he did not want.

In a clear reference to President Reagan's desire to have that declaration endorse the U.S. zero-option and interim accord proposals offered at negotiations in Geneva on reducing medium-range nuclear missiles in Europe, Mitterrand said that the conference had turned back efforts "by some to engage France in decisions that she is not a part of."

Moreover, he said that the summit leaders had apparently learned from "the unhappy experience of last year" when disputes at Versailles over East-West trade provoked severe strains in the western alliance.

This year, he said, they had "demonstrated good will" in adopting a softly worded, brief reference to the need for "East-West economic relations to be compatible with our security interests."

"There were no long debates on this subject this year," Mitterrand said. "Last year, we talked about it too much and not exactly as we should have."

Before leaving Paris last week, Mitterrand said that he was going to Williamsburg "without illusions," and he echoed that phrase today. He made it clear that he had been determined to disprove predictions in the media of a major U.S.-French clash.

Elected in 1981 after two failed attempts to become president, the French Socialist leader "knows how to come back from defeat," one French official said after the news conference. "He lost at his first two summits, in Ottawa and in Versailles, and he knew he had to be firm here without being polemical or antagonistic."

Mitterrand indicated that he knew when to yield here by saying that he had wanted to press for a summit commitment to stabilize commodity prices in international markets. "That would have taken another day, and that was not scheduled. I did not fight much," he said.

He described the summit's final declaration on economic recovery as a reasonable compromise "that went further than the pessimists had said but did not go as far as I would have liked."

He said that he is satisfied with having made his point that the high value of the dollar, which reached record levels against the franc during the summit, is damaging France and the rest of the world, including U.S. export possibilities.

His ideas for an eventual high-level monetary conference "began to penetrate here," he said, and he pointedly noted that the French language on the proposal to study such a conference was adopted in the final communique.

He cast his recent suggestion for holding a "new Bretton Woods" monetary conference as a long-range call for fresh thinking on ways to find "not fixed but stable exchange rates."

He said continuing overvaluation of the dollar--"when the world economy goes well, it rises, and when things go poorly, it rises"--demonstrates the need for "a more supple instrument" as a reserve currency. "But it will be up to the experts to define" such a device, he said.

French officials said Mitterrand had no trouble agreeing to an annex drawn up by finance ministers on fighting inflation since he can use it at home as an endorsement for his austerity plan. It has been criticized by his conservative opponents and by communist coalition partners.

Mitterrand suggested that the strongest arguments here involved "the initiative of Mr. Reagan" to have the summit issue a statement endorsing U.S. arms-control proposals and asking the Soviet Union to negotiate more seriously at Geneva.

Ironically, Mitterrand had shifted French policy dramatically when he first came to office by endorsing Reagan's general nuclear rearmament program. He specifically backed NATO's decision in December, 1979, to begin deploying 572 U.S. Pershing II and cruise missiles in western Europe this December unless the Soviets agree to dismantle their medium-range missiles targeted at western Europe.

"The final declaration contains nothing beyond what France has already said. And it contains no new elements that could complicate negotiations" or make it appear that France is again becoming part of NATO's integrated military command, from which it withdrew in 1966, he said. France blocked even a mention of the December, 1979, NATO decision in the summit statement.