After four years of preaching the gospel of Reagan's America in Socialist-governed France, Evan G. Galbraith wound up a controversial tour as U.S. ambassador here today with a call for major reforms in the Foreign Service, including nomination of political appointees to all major U.S. embassies and senior positions in the State Department.

Such a step was necessary, he said, to correct what he depicted as the Foreign Service's built-in "liberal Democrat" bias.

Insisting that foreign policy should be formulated by the president and not the State Department, Galbraith, in his last interview before leaving Paris, said it was particularly difficult for a conservative president such as Reagan to find ambassadors who shared his convictions from the ranks of the professional Foreign Service.

"The facts are that most of the people in the Foreign Service vote Democrat. I can't verify it. It's just a feeling I have. The conservative Ronald Reagan took that office without a great deal of support or enthusiasm from the Foreign Service," he said.

Galbraith, a banker and staunch conservative, has attracted admiration, anger and ridicule here for his outspoken comments on French political life. He also has provoked protests from the State Department and his embassy staff for disparaging remarks he is reported to have made about career diplomats.

The envoy made a spirited defense of his "public diplomacy" in the interview. He also looked back with satisfaction on the improvement of French-American relations that has occurred during the past four years despite sharply different ideological outlooks.

He depicted the diplomatic storms of the 1960s as caused by France's resentment of its perceived second-class status in a postwar world dominated by the United States and the Soviet Union.

So strongly does Galbraith feel about reforms in the Foreign Service that he is writing a book -- a plea for "public diplomacy" by politically committed ambassadors.

Galbraith, 57, a former vice president of Morgan Guaranty Trust, said ambassadorships in all major overseas posts should be reserved for political appointees. He called for the president to appoint "his own men" to key State Department positions.

"All assistant secretaries should be the president's men. It the State Department is too big a place to rely on the secretary and the deputy secretary to enforce the political policy. It's got to go down to the bureau level where options are formulated and talking points are discussed," he said.

A 1982 survey showed 48 percent of Reagan's ambassadorial appointments and 37 percent of Jimmy Carter's were political.

Last February, Galbraith was rebuked publicly by Secretary of State George P. Shultz after he was reported by The New York Times as saying that the Foreign Service "takes the guts out of people."

"He should have his tongue tied for him," Shultz said. Galbraith later said his views had been distorted.

Alluding to past controversies, Galbraith said that he accepted that there was "a risk involved" in speaking out.

"Things that you say may be turned a little bit. You may misspeak on a phrase or two, you may rub someone in a way which causes a counterargument. It's not without risk, public diplomacy," he said.

Galbraith will be succeeded as ambassador to France by Joe M. Rodgers, the head of a Nashville construction company and prominent Reagan fundraiser. Unlike Galbraith, who lived in France in the 1960s and frequently gave interviews in French, Rodgers does not speak French.

Asked about his successor, Galbraith said that he fulfilled the two essential requirements for an ambassador: he is intelligent and closely identified with the president.

"He'll work on making himself understood," he said.

Some of the biggest rows touched off by Galbraith during his four years in Paris arose from his publicly expressed contempt for the French Communist Party, a junior coalition partner in President Francois Mitterrand's Socialist-led government until July 1984. He was summoned for a dressing-down by the then-prime minister, Pierre Mauroy, in February 1984 after he described the Communist minister of transport as "a poor Frenchman gone bad."

The transport minister retorted that Galbraith was "vulgar and stupid." The ambassador was applauded, however, by right-wing newspapers and politicians.

Reflecting on the French political scene during the past four years, Galbraith said that the alliance with the Communists served a tactical purpose for Mitterrand. The decision to admit four Communist ministers into the government in June 1981 was initially criticized by the Reagan administration, which said it feared that their presence might jeopardize western security.

"That was one of my first missions: to look at Mitterrand's decision to admit the Communists , analyze it and explain it back to Washington," Galbraith said. "It wasn't a true coalition, but a political payoff of the kind you might find in city hall in the U.S. I was able to convince my government that the influence of the Communists on Mittererrand was, for practical purposes, zero."

Noting that Mitterrand had gone much further than his conservative predecessors in supporting the deployment of U.S. nuclear missiles in Western Europe, Galbraith said there had been a remarkable change in French attitudes toward America in the past few years and anti-Americanism had died along with Marxism in France in the 1970s.

Asked whether the pendulum could ever swing back, he said: "Under my analysis the swing back won't be far. We have a common goal which overrides everything else, namely the defense of Western Europe. [Neither France nor the United States] can allow the Soviet Union to dominate Western Europe, nor allow the neutralization or demilitarization of West Germany."