After 37 years with the state-owned Renault auto company, Bernard Vernier-Palliez is beginning the diplomatic career he says he always wanted, as ambassador of the Socialist government in Paris to the business-oriented Reagan administration in Washington.

For a non-Socialist and a nondiplomat, the assignment could seem formidable. In a country that prides itself on the professionalism of envoys abroad, it could seem unusual. But for Vernier-Palliez, 63, it comes as a logical extension of France's growing investment in the United States and President Francois Mitterrand's concern for the health of his export industries.

"I think the business approach is now more important," Vernier-Palliez said in an interview shortly before his departure for Washington Friday. "Second, I think people who have been in business have a lot of contacts in the industrial establishment, which increases their means."

Vernier-Palliez has established his contacts in frequent travels to the United States, at least one trip a month in the last few years. But by his own account, he knows his way around Detroit better than Washington. This marks a clear distinction from the outgoing ambassador Francois de Laboulaye, a skillful career diplomat who spent enough of his youth in the U.S. capital to play on an American high school football team and who arrived back as ambassador in 1977 already knowing the key players and dossiers at the White House and State Department.

The cadence of Vernier-Palliez' recent travels to the United States reflects Renault's increasing investments in U.S. firms, part of accelerating French investment in the United States estimated by economists to have reached $8 billion in the last several years.

In his five years as Renault's chief executive, Vernier-Palliez steered the company to put $350 million into a 46 percent interest in American Motors Corp., $84 million into a 20 percent interest in Mack Trucks Inc. and a yet-to-be-determined sum into a joint venture with Ransburg Corp. for an enterprise called Cybotech.

Perhaps not coincidentally, the new American Motors president named last week, Jose J. Dedeurwaerder, arrived at the U.S. firm only last fall--fresh from Renault's plant at Douai in northern France.

It is at the Douai factory that Renault pioneered the use of robots in auto manufacturing. The Renault-AMC combine plans to use such robots in building the Renault R9 sedan beginning next summer at Kenosha, Wisc., on Lake Michigan. And, closing the circle, robots are to be the main product of the Cybotech joint venture with Ransburg.

Engineering such conquests, Vernier-Palliez says, kept him immersed in foreign affairs despite his job as a car maker. But not all Renault's foreign operations have been such successes. A 40 percent holding in Iranian firms assembling R5 Renaults was taken over by the revolutionary government in Tehran.

"If you head a multinational company, the most complicated problems you have to face are the political problems around the world," he recalled in his austerely furnished office overlooking the Champs Elysees. "You have to give them a lot of time and attention."

Since Jan. 1, Vernier-Palliez says he has stopped giving them attention for Renault and has broadened his concerns to include French interests in general, including former competitors such as Peugeot and Citroen.

"Since I left Renault at the end of the year, I am no more interested in Renault than in Peugeot," he said, smiling. "I am interested in the expansion of French industry."

A native of Tours in central France, Vernier-Palliez speaks a precise and richly accented English that makes "robots" sound like "rowboats."

As a newcomer, Vernier-Palliez plans to spend at least a week with de Laboulaye in Washington. Despite their different backgrounds, the two men are good friends.

The auto executive-turned-diplomat originally wanted to start out as a diplomat. He attended the prestigious school of Hautes Etudes Commerciales and moved on to the Ecole Libre des Sciences Politiques, intending to take an examination for entry into the diplomatic corps.

"I started in 1937, but it was very bad planning, because just as I was finishing, the war broke out," he recalled.

The hostilities and France's occupation by Nazi forces led him to slip out of France via Spain to join Charles de Gaulle's forces in northern Africa. He was part of the French Expeditionary Corps that fought with the U.S. 5th Army in Italy under Gen. Mark Clark.

As the war wound down, he still looked forward to a diplomatic career. But a friend told him he would be demobilized more quickly if he agreed to join the just-nationalized Renault company.

"So in May of 1945 I came to Renault," he said. "I had the intention of spending a few months, but I ended up staying 37 years."