Secretary of State Cyrus R. Vance and French Foreign Minister Jean Francois-Poncet met today to discuss U.S.-French differences over the crisis in Afghanistan, but their talks were upstaged by the U.S. ambassador in Paris, who characterized some French foreign policy attitudes as "neutralist nonsense."

In a speech yesterday, Ambassador Arthur A. Hartman focused on the divergent views among the allies that are blocking a concerted strategy toward the Soviet invasion of Afghanistan.

Then, in a direct reference to France, which has been the country most resistance to U.S. policy views, Hartman said: "It seems to me important not forget what side you're on."

Harman's speech underscored the hostility that has been building up between the Carter administration and President Valery Giscard d'Estaing's government in the two weeks since loud French opposition forced the scutting of a planned meeting in Bonn between Vance and the foreign ministers of America's major NATO partners to discuss Afghanistan.

Instead, Vance made fast-paced visits to different European capitals. After talks yesterday in Bonn and Rome, he met in Paris this morning with Francois-Poncet and then came to London to see the British foreign secretary, Lord Carrington.

Although Vance went out of his way to describe the Paris meeting as "very cordial" and "useful," he also admitted: "There were some differences between us."

Vance refused to discuss the specifics of U.S.-French differences. But they are known to stem from the French view that U.S. efforts to penalize the Soviet Union for the invasion and to contain further Soviet moves in the Persian Gulf region could irreparably damage the move toward East-West detente and put Western Europe under the shadow of a new cold war.

Although this concerns is shared somewhat by other allies such as West Germany, France, which cherishes what it regards as "a special relationship" with Moscow, has put the greatest distance between its position and that of the United States.

The Giscard government has opposed strongly the U.S. attempt to organize a boycott of the Moscow Summer Olympics. France argues that the West should avoid confrontation and seek to resolve the Afghan situation through negotiation that will preserve the fabric of detente.

But, while Vance publicly took a low-key and conciliatory stance in Paris today, the Hartman speech, which U.S. officials pointedly called to the attention of reporters traveling with Vance, indicated that Washington also does not mind using brass knuckles to make its point.

Hartman's speech was aimed at remarks made recently by Michel Poniatowski, a former French interior minister who is regarded as Giscard's closest confidant. Although Poniatwoski is not in the French government now, it is considered unthinkable in France that he would advocate any important policy ideas without Giscard tacit blessing.

In a recent speech, Poniatowski argued that French and Western Europe should disengage from the quarrels between the United States and Soviet Union, band together to build their own collective nuclear deterrent and follow an independent course.

That led Hartman, in a talk to the American Club of Paris, to say: "The statements of certain political figures that Europe should be 'de-NATO-ized' and that France should find 'a new way between the two superpowers' can only be characterized as smacking of neutralist nonsense . . . It seems to me important not to forget what side you're on."

In other references to the French position in the Afghan situation, Hartman said: "Many of those in Western Europe who today are whispering about American overreaction would have been there to cry over the United States having 'lost' another country."

Citing the need for "a united Western approach," Hartman said: "We do not ask Europe mindlessly to align itself with us: but we have a right to expect Europe not to distance itself from us simply to show its independence." e

Hartman is a career diplomat who, before the Paris assignment, was assistant secretary of state for European affairs. Although U.S. officials said Vance had not seen his speech in advance, it was known that Vance was aware of its tone and contents.