Paul Berenger, a charismatic politician described by his opponents as both a Marxist and a friend of big business, is testing whether a Mauritian from the tiny segment of the population that is descendent from the early French colonizers can be elected prime minister of this Indian Ocean island.

Berenger, 38, is the focus of a divisive campaign for the parliamentary election Aug. 21 that revolves around the turbulent ethnic politics of this polyglot nation, 1,100 miles off the coast of southern Africa, with a tradition of fierce democratic politics.

Mauritius, a western diplomat said, "is the damndest boiling, churning laboratory of democracy you can see," based on a wide variety of communal groupings including Hindus, who make up more than 50 percent of the population; Moslems; Creoles (people of mixed race), and the small percentage of Chinese and the whites of European descent.

Last year Berenger's leftist Mauritian Militant Movement, subordinating ethnic interests to ideology, swept into office with a coalition partner. The victors won all the seats in parliament and ousted Sir Seewoosagur Ramgoolam, the octogenarian, pro-Western prime minister who had held power since the country gained independence from Britain in 1968.

Although Berenger was the leader of the party, the movement abided by the tradition that the prime minister must be a Hindu, and Berenger put forward his ally Aneerood Jugnauth as prime minister. Berenger, from the 2 percent white minority, became finance minister.

The expectation was that Jugnauth and Deputy Prime Minister Harish Boodhoo, leader of the coalition Mauritian Socialist Party and also a Hindu, would be figureheads carrying out Berenger's policies. But they had other ideas.

Political differences caused the unanimous coalition, based on socialism and nonalignment, to disintegrate in nine months. The glue of ideology was not enough to hold the alliance together under the pressures of ethnicity and what his opponents call Berenger's dictatorial style. Jugnauth and Boodhoo formed a new party and joined forces with two former enemies, Ramgoolam's Labor Party and the right-wing Social Democrats, to run against Berenger.

The campaign puts Jugnauth and Boodhoo in the strange position of criticizing the action of the government they led, but they heap the blame on Bergener's economic measures.

With Bergener running for the premiership after Jugnauth dissolved parliament last month, issues of race and personality are out in the open in this island of 1 million people living in an area smaller than Rhode Island.

"I am used to be being the focus," said Mauritian-born Bergener, who broke into politics on the street barricades during the 1968 riots in Paris where he was a student.

He returned to the island and quickly became a controversial figure as he sought power through organizing trade unions. After a series of crippling strikes, Ramgoolan declared a state of emergency in 1971 and imprisoned Berenger for a year.

Berenger, however, has pushed his militant image into the background during the past year, suggesting instead the role of the modern economic manager. In an interview, Berenger displayed his notorious sharp tongue.

"Our problem," he said, "is that the prime minister has no knowledge of economics and the deputy prime minister is a fool."

Berenger is a little less precise when asked about his penchant toward Marxism.

His party's landslide victory last year produced headlines in the West proclaiming a Marxist victory, but little recognizable Marxism resulted. "I've never been a Marxist," Berenger said. "The MMM has never been a Marxist party."

Then he changed tack, saying, "We've always been clear-headed Marxists. We analyze society in terms of classes."

The movement was the first major party in Mauritius not to be organized on ethnic lines, although it is usually careful to run Hindus in Hindu-dominated constituencies. "We replaced race warfare with the class struggle," Berenger said.

He dismissed the politics of Marxism, saying he was opposed to a one-party state and he added: "I don't think that Marxism has much to teach us in the economic sphere." He described himself as a modern Democratic Socialist who is "very, very management-minded."

Whatever he is, Berenger made the business community happy during his nine-month tenure as finance minister, impressed officials of the World Bank and the International Monetary Fund and infuriated his erstwhile allies with a one-man act in which they felt he turned his back on the masses.

Boodhoo best summed up the opposition to Berenger, saying, "He's neither a Marxist nor a capitalist. He's a Berengist."

Gaeton Duval, a long-time bitter enemy of Berenger and a leader of the Social Democrats, which is the power base for Creoles, was straightforward about the racial issue.

"Mr. Berenger is an ambitious man," he said. "No matter how ambitious a white may be, in the political circumstances in Mauritius he must play second fiddle . . . . Only a Hindu can be prime minister."

Duval acknowledged that "ethnic politics are bad. We've gone back 20 years, but it is because of the ambition of one man. Berenger has alienated Hindus so much he's brought them together. They'd support anybody but Berenger. They'd even support me."

Jugnauth, Boodhoo and Ramgoolam all steered clear of ethnic politics in interviews, instead emphasizing Berenger as the issue.

"Anybody can be prime minister," Jugnauth said. "Anybody who knows how to play the game and get the confidence of the people. Berenger has failed miserably."

Ramgoolam said Berenger "would be a disaster for Mauritius." He charged Berenger "wants to run this country on the basis of communist Russia"--rule by one party.

So far, the focus on Berenger seems to be hurting him in the campaign. Berenger said, however, that the "very personal, very negative appeal to hatred will rebound in our favor" before the elections next month.

Explaining his economic policy shift, Berenger noted Mauritius' public debt of about $700 million and said: "Right now we are a colony of the IMF and the World Bank and we'll remain so for a number of years until we get back our independence through sheer work."

"The people understood, parliament understood a bit less and some of my colleagues not at all," he said.

Last autumn in Washington he negotiated a $45 million loan from the World Bank to prop up the recession-plagued economy and worked out a standby loan from the IMF for about $60 million.

In return they demanded measures that were bound to be unpalatable for a leftist government: increases in sales taxes, decreases in food subsidies and a reduction in the export duty on sugar.

The uproar over the economy finally led to Berenger's resignation in March and the shifting of alliances in preparation for elections called by Jugnauth.

Many business leaders fear that the economy will stagnate further if the new alliance wins because, as one said, it is "a dog's breakfast of bitter enemies," and they will be at each other's throats within months.

One businessman who was a bitter foe of Berenger during labor union strife in the 1970s said that the Mauritian Militant Movement now offered stability.

"When Berenger got power a change came over him. He saw the problems of the economy. The fact that he contributed to the problems was another matter," the company manager said. "He is up earlier and to bed later than the others. As for his reputation for being dictatorial--in another place people might simply say he wants to get things done."

Several other businessmen expressed similar opinions. Whether this will profit Berenger on an island where most people are descended from Indian coolies or African slaves--but whites still control the economy--will only be known Aug. 21.