France's Socialist government is dispatching as its new ambassador to the United States a man likely to bring sharp changes in the style of French diplomacy in Washington -- a nondiplomat reputed to be a homebody who has spent his entire career with the nationalized Renault auto company.

President Francois Mitterrand's choice of Bernard Vernier-Palliez, 63, demonstrates official confidence in an executive who has helped make Renault into Europe's leading automobile manufacturer and a paradigm that French Socialists point to repeatedly in explaining their reasons for nationalizing more French industry.

It also reflects a desire to underline the difference between Mitterrand and his predecessor, Valery Giscard d'Estaing, whose ambassador, Francois de Laboulaye, is, in the carefully chosen words of a French diplomat, "more of a society ambassador" than the party-shy Vernier-Palliez.

Officially, a Foreign Ministry spokesman explained that Mitterrand picked Vernier-Palliez "because he knows your country well" as a result of business contacts as chief Renault executive since 1976 and a steady career with the state-owned company that began in 1942 even before it was nationalized. The French press added that Vernier-Palliez's experience makes him an ideal advocate in Washington of Socialist nationalization programs, able to argue from firsthand knowledge that nationalized business can work.

In a twist of humor, the daily Le Matin pointed out that the French Embassy in Washington also will be a good platform for selling Renault's latest model, the R9, for which company officials see a bright future on the U.S. market.

A Foreign Ministry source emphasized that Mitterrand and Foreign Minister Claude Cheysson, both of whom know Vernier-Palliez personally, picked him as ambassador to Washington also as a gesture to mark a shift away from "the image of France as a country that sells perfume and has nice little women."

The burly Vernier-Palliez has made his reputation with balance sheets and production charts, acquiring a $350 million interest in American Motors and helping turn Renault from a sluggish state-owned behemoth into a decentralized money-earner that turns hundreds of millions in profits. In doing so, he followed a schedule that includes two days a week "on the ground" in Renault factories.

De Laboulaye, in contrast, is known as a smooth professional diplomat with equally smooth family connections that earned him entrance into France's ultra-select Jockey Club. His style and the image of France he represents, a Foreign Ministry official said, made him a likely target for Mitterrand and his Socialist government.

With his 65th birthday approaching next June, de Laboulaye was in any case scheduled for retirement, ministry officials pointed out. But sources said Cheysson has expressed willingness to leave him in place as long as possible to avoid the impression of chopping off heads in an unseemly way. Another consideration, they said, is that Vernier-Palliez is scheduled to remain as president-general director of Renault until the end of the year.

As chief executive at Renault, Vernier-Palliez has fled Paris society with determination. His associates say he enjoys opera in the evening and horseback riding on his days off but shies away from the demands of entertainment and social dinners

Although his appointment as Renault's top manager had to be approved by the government -- Giscard's at the time -- Vernier-Palliez never has been involved in politics, a Renault spokesman reported. Foreign Ministry officials said, however, that he knows Mitterrand and Cheysson from professional meetings and seminars in which the three participated.

French diplomatic appointments traditionally remain within the professional corps more than in the United States, although appointments outside of what the ministry calls "the career" are not extraordinary. Vernier-Palliez's appointment, expected to be announced officially after Washington agrees to it, thus aroused little open controversy here.

It came, however, as part of a shuffle that affected about 50 jobs, including some of the more prestigious that went to nondiplomats such as Vernier-Palliez. Among these is Francis Gutman, who has been in business since leaving the Foreign Ministry in 1957, after a seven-year stint. Gutman, most recently head of the French Red Cross, was named the ministry's secretary general, its top administrative office.

The association of National Administration School alumni, who consider themselves the cream of the French diplomatic corps, lodged a mild protest with Cheysson last month when the minister's plans to bring in a number of noncareer officials became known. While the group endorsed the principle of outside appointments, it focused on what it said was a danger of assigning the best jobs to noncareer appointees, leaving only secondary jobs for career diplomats.

Chief among their worries was the embassy in Rome, the Farnese Palace designed by Michelangelo, known in the French corps as a plum. The winner of that job, it became known here this week, is Gille Martinet, a journalist and longtime colleague of Mitterrand's in the Socialist party, but not a diplomat.