Mauritius, a tiny island in the Indian Ocean, is a nation of paradoxes.

Sir Seewoosagar Ramgoolam, the 83-year-old former prime minister, highlighted the contradictions unintentionally when he criticized his political opponent, Paul Berenger, as "too dictatorial."

"This is not Africa, where dictatorships are the rule," Ramgoolam said in an interview, ignoring the fact that he was chairman of the Organization of African Unity in the mid-1970s.

Actually Mauritius, which dots the Indian Ocean 1,100 miles off southern Africa, is a melting pot for three continents--Asia, Africa and Europe.

Its polyglot mixture of 1 million people is crammed into an area only three-fourths the size of Rhode Island. With more than 1,300 persons per square mile (the United States has about 62 per square mile), it is one of the world's most densely populated nations.

Mauritius' small population is stunningly diverse:

* The country has 34 political parties, 255 trade unions and 400 bus companies.

* Although Mauritius was a British colony until 15 years ago (it is now an independent member of the Commonwealth), French and Indian influences dominate.

* The government radio broadcasts in more than a dozen different languages. English is the official language, but few people prefer it. Creole ("French without grammar") is the lingua franca; all six daily newspapers are printed in French, although two papers, The Nation and a weekly, The Star, have English in their names.

* The population is divided mainly along religious lines, with Hindus a majority. Blacks and whites are lumped together in the same population classification. Fearing domination by the Hindus, they joined forces in opposing independence from Britain 15 years ago.

About 68 percent of the population is of Indian descent, 52 percent Hindu and 16 percent Moslem. Blacks and Creoles (persons of mixed race) make up 27 percent, and are combined with whites, about 2 percent of the population, in a grouping called the General population. The remaining 3 percent are people of Chinese descent.

ALTHOUGH ALL MAJOR parties favor the country's becoming a republic, Mauritius is Britain's only former African colony that still recognizes Queen Elizabeth II as the monarch.

Part of the variety here stems from the fact that the island had no indigenous population. It was settled by the Dutch in the 17th century. They abandoned it, and France claimed it in 1715.

The island was the scene of the only French victory over Britain's Royal Navy during the Napoleonic wars, the battle of Ville Grand Port, duly inscribed on the Arc de Triomphe in Paris. Not so a later battle, in 1810, which led to British control. The British ruled with a light hand and let French traditions remain.

Britain, however, did outlaw the French practice of importing slaves from nearby Madagascar and instead brought in indentured laborers from India, thus bringing about the Indian dominance.

WHEN A LEFTIST, nonaligned government was elected last year, there was every reason for relations with the United State to sour. The Reagan administration had sought to use food aid to help keep Ramgoolam in office.

In a rare move, the U.S. Agency for International Development allowed the Ramgoolam government to sell $2 million worth of food aid and use the proceeds to employ thousands in make-work projects just weeks before the election.

"There is no question but that the United States took sides in the election," a diplomatic source said.

It made no difference; Ramgoolam was swept out of office in a landslide, his party not winning a single seat in parliament.

Nevertheless, U.S.-Mauritian relations have kept on an even keel. Last month the State Department acceded to a Mauritian request that U.S. Ambassador Robert Gordon, dean of the tiny diplomatic corps and long due for transfer, stay through hotly contested parliamentary elections next month.

The new government moderated campaign pledges to stop the national airline from flying to South Africa, the most profitable route.

QUIET DIPLOMACY resulted in reversal of a policy forbidding port calls by U.S. Navy ships. Three calls in recent months gained Mauritius more than $125,000.

Demands for Mauritian sovereignty over the British island of Diego Garcia 1,200 miles to the northeast, where the United States maintains important air and naval facilities, are still an issue, at least rhetorically. But many officials acknowledge that the U.S. facilities for the Rapid Deployment Force are a fait accompli.

"It won't disappear by our mere asking for it," said Prime Minister Aneerood Jugnauth in an interview. "We have to be practical."

That has meant negotiating an agreement with Britain to provide more than $6 million to aid displaced former residents of Diego Garcia who now live in poor conditions in Mauritius.

Diplomats acknowledge that Mauritius will continue to trumpet the issue of sovereignty over the tiny horseshoe-shaped atoll, if for no other reason than to maintain its credentials of nonalignment.

But it is hard to take the issue too seriously on this lush tropical island.

Last year when Britain was fighting to recapture another outpost of empire, the Falkland Islands, it was suggested jokingly here that Mauritians drive the British out of Diego Garcia, using sugar-cane stalks.