Maurice Templesman, an American friend and business associate of President Mobutu Sese Seko, and reputedly a person of influence in this country, had a say in the recent appointment of the new U.S. ambassador to Zaire, acording to one U.S. diplomat here.

In fact, the diplomat said, the local American business community knew about the appointment of Robert Oakley even before the U.S. Embassy did.

In Washington, such views of Templesman's role are described as exaggerated if not utterly wrong. But in Kinshasa, the New York diamond and metals businessman is viewed as a mover and shaker with important political ties to both Democratic and Republican organizations back home.

It was Templesman, sources here said, who put together the international combine that owns 80 percent of the world's richest copper and cobalt lode, lying under 900 square miles of savanna just outside Kolwezi, in Zaire's mineral-rich Shaba Province.

The rest of Zaire's mining operations in the area's is owned by gecamines, the government company, which is forbidden to touch the rich lode. The story of how the wealth nearby came to be owned by outsiders provides a rare glimpse into the labyrinth of interlocking relations between industry and government in developed nations, and a Third World dictator.

Those who know Templesman say that he "grew up in African metals" as a salesman, middleman and investor. His father had established the firm of Leon Templesman & Son long before independence fever swept Africa after World War II.

Maurice Templesman, according to one diplomat, shrewdly anticipated Africa's changing political tide in the late 1950s and early 1960s and began to "move in with the new regimes." Today, his firm has branch offices throughout West Africa, dealing primarily in diamonds, but including metals as well.

Templesman's involvement with Mobutu dates back to the 1960s, when Mobutu was looking for market's for Zaire's industrial diamonds. According to U.S. diplomatic sources, both men share business interests in Zaire's two main diamond mining concerns, MIBA and Britmond.

U.S. Bureau of Mines figures show Zaire as the world's principal producer of industial diamonds. More iportant, howevr, are Zaire's reserves of the world's total industrial diamond reserves estimated at 680 million carats, more that 500 million are located in Zaire's south-central Kasai province. Total yearly export sales in industrial and gem diamonds from the two companies run into the hundreds of millions of dollars.

Mobutu's rise from a salaried army officer in 1965 to one of the world's richest men is mainly the result of his personal control of Zaire's diamond exports, Western officials say.

The exact nature of Templesman's involvement with Mobutu is not known. Templesman's office in New York would not disclose even general information about him. But a diplomatic source who knows both men describes their relationship as "very personal" and said that both are reaping substantial earnings from the gem diamond trade. a

When Mobutu sought to put together a second copper mining company in Shaba province t offset Zaire's total reliance on Gecamines, he turned to Templesman. According to business sources here, Templesman brought together foreign investors from the United States, France, South Africa and Japan to form the Tenke Fugurume Mining Society, in which he and Mobutu also each have a personal share.

The Templesman group is represented in Kinshasa by Larry Devlin, a retired Central Intelligence Agency official who served as the agency's station chief when Mobutu came to power in a 1965 U.S. supported coup. Devlin's assistant is Col. John Gerrassi, who formerly headed the U.S. military mission to Zaire.

"Larry can talk to Mobutu any time he wants to," said a Western source who knows Devlin. Devlin, who operates out of a third floor office in Kinshasa's Texaco Building, was unavailable for comment.

After an initial investment of $250 million for roads and down payment on mining equipment, tenke Fugurume now needs an estimated $400 million more to start assembling the plant.

The project has been stymied since 1976, when the Benguela Railroad, which gives the mining region in southern Zaire access to seaports in Angola, was closed during the Angolan civil war. It remains closed because of antigovernment guerrillas operating in the neighboring country.

One investor, Standard Oil of Indiana, recently sold its 28 percent interest to a French government mining company. Standard apparently was frustrated by the continued disruption of the crucial railroad.

Templesman is believed to have helped Mobutu with advice on political matters in Washington Mobutu's lobbyist in Washington is William Blair, former U.S. ambassador to Denmark and the Philippines and one-time law partner of Adlai Stevenson.

Templesman has made campaign contributions to both Republicans and Democrats. In 1972, he contributed $5,000 to Richard Nixon's election campaign.This year he gave $1,000 each to the reelection compaigns of Sens. Frank Church (D-Idaho) and George McGovern (D-S.D).

In Zaire, Templesman's influence is considerable. "Things get very personal here," said a senior diplomat, "and to get along with the chief of state is all that matters."