In Jamaica, Prime Minister Michael Manley is a hero to toothless teen-age boys who used to waste their time in shantytown bars, to women sore-scarred from giving painful birth on piles of leaves, to college-educated taxi drivers tired of what they do.

When Manley was 18, a senior at an exclusive Jamaican prep school, he had an argument with his British schoolmaster about the plight of such people in Jamaica, a country whose enormous wealth was conspicuously enjoyed by a few.

"He threatened to expel me," Manley said during a recent interview, recalling what he figured to be the most significant event in his life.

"I told him he couldn't expel me because I resigned. So I did, packed my bags and left."

So he did, but not without talking all of the other students into packing up with him, and, in effect, striking for three weeks until the schoolmaster was replaced.

Manley is 52 now, but there is still much of that radical prep-school student in him as he attempts to mobilize a large and diverse Jamaican population for its sixth year of democratic socialism.

With Manley-introduced democratic socialism in 1974 - two years after he was first elected prime minister - taxes on American bauxite companies were levied, the transportation industry was nationalized and remaining plantations were broken up. Thousands of farmers were set up on farm cooperatives, work projects were established to curb unemployment and health and education were made available to all, rather than the privileged few. Manley also pushed for a system of racial equality that now offers educated blacks the same opportunities as whites.

It is a brand of government that has received mixed reviews internationally and which Manley, while contending it is the best for Jamaicans, concedes is in serious financial trouble.

Noting that there are 2 billion poor people living in the Third World, Manley says he wants a new international economic order.

That is why he came to Washington, to talk to President Carter about establishing one.

Manley is a tall, lean man with oak-like arms and a barrel chest. When he shook hands with men upon his arrival in Washington, he crushed their fingers. For women, he offered a stiff, "Howdy, ma'm"-styled bow from the waist, kissed their hands and grinned boyishly when jubilant young Jamaican women students swooned.

"I am fond of people: It's as simple as that," Manley says modestly of his extraordinary charm. "It just so happens that people are kind enough to be fond of me. It's funny, I've always been like that - I wasn't known as a charming kid. More as a horror.

"But I've always seen people as people, not just as categories as so many others in Jamaica used to do."

As he talks, Manley leans forward intently, sitting backwards suddenly in his seat as he changes subjects.

"We're going through some very tough times now. Great sacrifices are being made. We have no need for frivolity in Jamaica today. No more Cadillacs, Mercedes or cornflakes. People need food, clothes and medicine," he said.

It is easy for Manley to conjure up images of Jamaica as it was when he was a boy. And it is also hard.

He squints his eyes and wrings his hands as he begins. "I remember my youth spent in the very heart of the colonial experience - remembering growing up aware of a world dominated by colonialism and racism - remembering the inner psychological experience, the implied political and social impotence of being a victim of both these experiences which between them provided the cultural parameters within which I was born.

"From the perspective of a now-independent nation, one might be tempted to forget. But the truth is that my generation will never forget. Nor should any Jamaican or black person, or indeed any person, forget those who pioneered the way to freedom and who made their lives a gift for the liberation of others."

Manley had several purposes on his mind as he moved through Washington from Thursday to Sunday - talking to President Carter and Secretary of State Cyrus Vance about terms of international trade, to the press about criticism that his government is too leftist, and to Jamaican nationals about defending the country against its detractors.

It was a low-keyed trip, overshadowed by the visit here of Israeli Premier Menahem Begin. It was not the illustrious occasion that some Jamaicans who had helped plan his visit had hoped for.

Because Begin was put up in the prestigious Blair House during his stay and Manley was put up in the Embassy Row Hotel, some Jamaicans who live here complained that they felt Manley had been slighted.

But the end of the visit seemed to be most fitting as a crowd of several hundred Howard University students, who had just organized a Jamaica National Association, enthusiastically cheered Manley's visit to Howard and his speech to them.

"We are the definitive voices of the Third World," he told the students, "and it is not only your country's image at stake. I am not asking you to be a propagandist," he said pounding the podium, "just defend your rock . . ." The crowd roared enthuasistically.

"Rarely do you find a man who knows what he's about like the P.M.," said Grace Marshall, a Jamaican nurse who works at D.C. General Hospital and who attended Manley's speech at Howard." He knows how to deal with all kinds of people. He can talk to England's prime minister about economics and still talk to the man on the street." she said.

Showing his ever-present sense of humility, Manley retorts, "The Rastifarian (a religious sect in Jamaica who advocate going back to Africa and are characterized by long braided hair) is the only Jamaican who really knows who he is with absolute certainty. The true Rasta has a calm certainty about himself and his place in the general scheme of things that is not true of his agitated brothers, like myself, for example.

Manley says he has been agitated for a long time. "Even at this prep school, the Jamaica College, that I used to go to, there was a magnification of all the worst elements of elitism.

"The kids of the rich always thought they were better than the poorer ones who got scholarships. The rich hung out in snide cliques, but the poorer kids were better educationally and in sports," Manley recalled.

The state of Jamaica before it attained independence in 1962 and for the 10 years after that, under the rule of the Jamaica Labor Party, was, Manley says, "Imperialist lackey."

When Manley took over the government, he felt it would be unwise - indeed, unnecessary - to break off ties with such countries as the United States, which still has over $1 billion invested in Jamaica, and decided instead to establish relations with Third World countries such as Cuba and Vietnam.

What Manley has ended up with is a government bureaucracy that is split: There are holdovers from the capitalist era in the intelligence service who converse with the CIA and there are new socialists who conceivably talk with Castro's agents.

Manley is the son of Norman Washington Manley, a Jamaican national ber, who began pioneering Jamaican independence when Michael Manley was 13.

"The family experience has been very important to me. But I don't know why any person in the political process thinks he does anything through politics. You begin with the conviction that you have to do something. Then you just start doing it."

"I decided to accept the challenge, and I have a deep feeling in the creative potential of man."