President Carter should have been in the tiny mountain town of Guayabotas last week. It was 94 in the shade, but a thousand cheering, emotional Puerto Ricans were stirring up the dirt yard outside a cockfight arena, straining to see an ancient man in a plaid shirt climb unsteadily onto the speaker's platform.

It wasn't much cooler up there, what with the press of bodies and the love flowing so hot you could see it, but Luis Munoz Marin, the 81-year-old founder of modern Puerto Rico, had come out of 14 years' retirement to deliver a message that President carter should have heard. It wasn't easy. Munoz had to wrestle every syllable past the mental roadblock that a recent stroke threw up against the speeches that hypnotized this island for more than 30 years. But he had to warn his compatriots, he said slowly, that asking for statehood would mean disaster for Puerto Rico and for the United States as well.

Munoz' reentry into public life is only the latest measure of the passion surrounding the question of whether Puerto Rico should ask admission to the union as the 51st state, declare itself an independent nation or remain more or less as it is, a "free associated state" in a commonwealth relation to the other 50. It is hard to find anyone among the 3.2 million Puerto Ricans jammed together on this tiny island who does not care one way or the other.It is equally hard to find anyone who does not think President Carter's future has become inextricably entagled with that of Puerto Rico.

The United Nations next week takes up the question of Puerto Rican status, reopening in its 24-member Committee on Decolonization a debate postponed from last year on a Cuban resolution that would declare the island a U.S. colony. Although such a declaration would not change life here very much, Carter would find it an embarrassment to his policies of human rights and moral leadership. While the administration will hold to its position that the U.N. committee has no jurisdiction in the matter, all the Puerto Rican factions have begun gearing up to use the forum as a way to complain that somehow the situation here must change, and soon.

Carter last month reiterated his support for self-determination for the island, vowing to urge Congress to grant Puerto Ricans whatever status they themselves decide they want. That careful neutrality may make him look anti-imperialist at the U.N., but he has become identified here with the pro-statehood forces, whether he likes it or not.

"Sure, he's with us, but we don't have any votes to help him out right now, so why should he stick his neck out?" reasoned Instruction Secretary Carlos Chardon, a member of the dominant New Progressive Party. "There's no way we can get statehood by 1980; that's a plain political fact." A Roadblock in Congress?

THE DIFFICULTY is that although the statehood tide is running strong now here, the waters in Congress might be decidedly chilly should debate ever get going on the subject. Puerto Rico is poor: nearly two-thirds of its people live on food stamps. It is determinedly Spanish-speaking; its admission would realign Congress, with two new senators and seven representatives - all Democratic - and 2 million voters.

Nationalist feeling also remains very strong here and statehood means cultural disappearance to many Puerto Ricans like Munoz Marin. Although his pro-commonwealth movement is divided and rudderless at the moment, it is not dead yet. Neither is the drive for independence, whose believers predict that violence will accompany any other course.

In short, Puerto Rico could become another Panama Canal flap for Carter, if he commits himself to grant something that Congress may be reluctant to deliver and that islanders do not universally want. Gov. Carlos Romero Barcelo, a dedicated statehooder, has pledged a referendum on the question of status here sometime after 1981, but the issue could come up sooner: Puerto Rico will hold the nation's first Democratic presidential primary in February 1980, one month before New Hampshire's.

Carter must have that date well in mind by now, since it was the 1976 Puerto Rican delegate selection that got him into all this. His aides probably had no idea they were stepping into statehood politics when they answered a letter back in November 1975 from one Franklin Delano Lopez, a San Juan public relations man. Delano Lopez wanted to know Carter's views on Hispanics and on Puerto Rico, he wrote, for consideration by his local Americans for Democratic Action chapter.

Delano Lopez, sounding as though he had rehearsed the speech, recited in an interview here a denial that Carter made any pledge to support statehood in return for the island's 22 convention delegates. Delano Lopez kept them from going to Sen. Henry Jackson as had been expected before New Hampshire; they eventually went to Carter and the rest is history. "We don't want Carter to endorse state hood," Delano Lopez said. "We want the people of Puerto Rico to endorse it. It's not for him to decide."

But before he hitched his wagon to Carter, Delano Lopez had been a statehooder associated with the island's Republicans. In fact, all statehooders have been associated with Republicans since it was party of Lincoln, much to the chagrin of many. That was because Munoz Marin invented the "free associated state" in the 1930s with the backing of the original Franklin Delano (Roosevelt), and supporter of commonwealth had run the island Democrats ever since. To be for commonwealth was to be a Popular Democratic Party member, a Democrat, and vice versa. To back statehood was to be a Republican, and vice versa.

But many statehooders felt themselves to be Democrats in spirit. Delano Lopez, who is described variously as a "clown" and a "genius," seized upon the McGovern reforms of 1975 that expanded party caucuses to launch the assault. To put it mildly, the traditional Democratic commonwealth backers resisted admitting people they had always regarded as Republicans.

"There were fistfights, people threw chairs . . . Delano Lopez wanted to disrupt things so Jackson wouldn't get the delegates. He was a Donal Segretti who succeeded," said Alex Maldonado, a commonwealth backer who is managing editor of the newspaper El Mundo.

After that, Delano Lopez rose to be Carter's field campaign cordinator for Hispanics, and was awarded a thank-you dinner in Washington after the election. His new Democratic party now controls the Democrats' future here; he is Carter's man on the island and a fervent statehooder still. "There may be citizens in the United States," he says, "who won't want Puerto Rico to be the strong polical force we will be as a state. Well, too bad for them. People there making decisions for us - that's over. We will either be a state or we will be independent, but no more of this."

Like other statehood advocates, he dismissed the opposition warning that Congress would humiliate Puerto Rico by refusing should it ever ask for statehood. International condemnation would know no bounds in that event, several persons said; Congress would not risk being charged with denying its citizens' appeal for equal rights and responsibilities due a former colony. The commonwealth party, left by his victory with no voice in the mainland politics, Delano Lopez waved into the historial dustbin: "They don't know what they are, what they want or where they're going." Problems of Progress

THERE IS CERTAINLY some floundering now among the Popular Democrats, the sort of indecision that, like a mid-life crisis, follows achievement of many early goals. The United States took Puerto Rico from Spain in an armed Invasion in 1898 and ran it for 50 years like the colony it was, granting citizenship in 1917, the vote for local offices only gradually and the vote for governor in 1948, when Munoz Marin was elected.

"I remember that the Republicans used to set up stands along here with free beer and music and a peso for everyone who would sell their vote," recalled Eusebio Vasquez Lozada, a pensioner, reminiscing near the cockfight pit as he watched for Munoz Marin to appear at Guayabotas. "I was just a little boy, but I remember 40 or 50 men standing here with machetes, waiting for one of the landowners to allow them to come and cut the sugar. We were slaves then . . . we were freed by Munoz Marin."

Munoz created the "free associated state" concept out of whole cloth when he decided, he said in an interview, that the island's total lack of natural resources would make his longed-for independence unworkable. The result is utterly unique.

"It's a tailor-made suit, and if you have a funny-looking body, you're going to have a funny-looking suit," explained maldonado, the pro-commonwealth editor.

Puerto Ricans, U.S. citizens all, use U.S. currency and the U.S. mails. They are defended by U.S. military bases that occupy 12 percent of the main and offshore islands. They have a Miami-like resort capital city. They hold local elections with U.S.-style hoopla and rhetoric. If the street life is very Latin tropical, with ancient fortresses, insane traffic, noisy markets, inept television and wonderful music, there are very un-Latin Yankee sanitary standards, good roads, federal courts and housing programs, and a free press.

Puerto Ricans sing their own national anthem before their own flag. Their bureaucracy works and so do their telephones. Living here, they cannot vote in U.S. national elections, but neither do they pay federal income taxes, and they may freely move to the mainland and establish residence to pay taxes and vote there. An estimated 2 million have gone, most to New York, but every state in the union has some Puerto Rican residents.

A third of all islanders, in fact, have lived "on the continent" for three years or more. All the parties claim the allegiance of those "neo-Ricans" who returned to live here, sympathizing with the discrimination they often suffer at the hands of those who weren't so poor they had to leave here too.

Commonwealth backers like to say the island has had the best of both statehood and independence without either the cultural strangulation or the bankruptcy they say one or the other would bring. Only commonwealth, they say, will allow fanatics of those two alternatives both to remain here in relative peace; only commonwealth will Preserve the tax breaks that enticed 2,000 processing and assembly plants to set up shop here.

With nothing to draw on but its energetic people, Puerto Rico produces 85 percent of the world's Valium among its many pharmaceutical exports, and 41 percent of all the canned tuna America eats. It is the seventh largest U.S. trading partner, sending and receiving more than $4 billion in goods every year. Although half again as poor as Mississippi in per capita income, Puerto Rico is more than twice as rich as the richest latin American country in the same terms. Troubled Economy

IT WOULD ALL still be just fine it it weren't for three hitches that developed in the last few years: population growth, the oil crisis and competing wages. Cheap imported oil ran all those factories and low-paid workers held the jobs, but when wages crept up and the oil flow stopped in 1974, so did the economy.

"Commonwealth was never ideologically based but was defined negatively as halfway between statehood and independence," said statehood backer Chardon. "It was based like other industrial economies on cheap raw materials from the Third World, and when the world changed, there was nothing to fall back on." The overcrowded island could prosper while excess labor went to New York, but when the immigrant flow reversed in the early 1970s, the crunch began.

Growing unemployment and hardship were the issues in the 1976 campaign, and they cost the Popular Democrats the election. They had tried, for the fourth time, to restructure the commonwealth system, but Congress balked at granting any more self-government. In fact, lame-duck President Gerald Ford ignored the "compact of permanent union" proposal for a looser alliance from a joint congressional-Puerto Rican study group and instead called for statehood in January 1977.

"That was the worst thing in the World for us. We wanted to keep the whole thing quiet until everything is prepared for the debate," said a pro-statehood Puerto Rican attorney in Washington. Gov. Romero's troops were caught with their arguments down and the bill went nowhere. Although Romero now says he would like debate to begin, his supporters indicate it can all wait until he and Carter are both reelected in 1980.

Romero at the moment looks like a shoo-in. One day last week, his helicopter descended out of the clouds into a dusty back lot in Ceiba, near the southeastern coast, bringing him to listen to local citizens' complaints as he does twice a month all over the island. The brawny governor, who looks like a silver-haired movie idol, was mobbed by eager citizens begging for autographs and he pumped every hand in sight.

The complaints in Ceiba, which abuts a major U.S. base, were economic: not enough books in the schools, crowded classrooms, bad docking facilities for the fishing boats, low-quality animal feed. Romero promised to do what he could, and town assembly member Corpulina Camacho Maldonado believed there would be changes. "He is wonderful," she said. "He is right about statehood. It would be a benefit for us in every way - salaries, health, schools, everything. We are proud to be Americans and we deserve our rights as citizens."

Statehood supporters argue that far from submerging Puerto Rica in a WASPish sea, a newly ethnic-conscious America would welcome the additional diversity as an opportunity to build new bridges to Latin America. "It could show the world that here is a Latin people who have been accepted in the United States as brothers," Romero said.

Although some businesses would leave without their tax breaks, many others would remain and new ones would come, according to Government Development Bank president Mariano Mier. While statehood would cost Puerto Rico about $175 million in new income taxes, the money would come back in spades: $1 billion in additional revenue sharing, Social Security benefits and other federal funding, supporters calculate. Independence advocates challenge the figures, saying the real cost to the United States would be $6 billion annually. A study team of the General Accounting Office and another cabinet-level group headed by Commerce Secretary Juanita Kreps and now evaluating the economic impact statehood might have.

Puerto Rico's resident commissioner in Washington, Baltasar Corrada del Rio, shrugged at the label "welfare state." He pointed out that Washington already sends the island $680 million a year in food stamps, more than double the California allocation, to one-eight as many people. "At least under statehood wealthy Puerto Ricans would be helping to defray the cost. Now we get it without paying anything."

The food-stamped citizenry means that if a plebiscite were held today between independence and statehood (excluding the commonwealth option), summed up Chardon, laughing, "We would get 80 percent: the 65 percent of the population that's on food stamps and the 15 percent that's middle class." His tally, it seems, is not just a joke.

Still, Romero has his problems, notably a reputation that he is ruthless to political critics and has fired too many Popular Democrats from government jobs. He has been criticized for leaping to defend several policemen now under investigation for gunning down two suspected terrorists, but he stuck to his view. He has a riveting personality that disarms the skeptical, and he maintains solid control of his party.

In an interview, Romero, who is 46, admitted an interest in holding a future Senate seat from his future state.His backers even see him as a potential vice president someday. "His personality fills the room. He's 100 percent political," sighed an opposition journalist. "The only hope for the Popular Democrats is to keep themselves together to pick up the pieces if Romero should falter." The Divided Democrats

UNFORTUNATELY for the Popular Democrats, they have not kept themselves together. After losing the proposed "compact of permanent union" and the 1976 election, Gov. Rafael Hernandez Colon quarreled with the grand old man, Munoz Marin, over whether the party should fight it out with Delano Lopez' rump Democrats in the upcoming October balloting for seats at the state Democratic convention.

Munoz opposed it on grounds such involvement in party affairs was too state-like. He won, and Hernandez Colon then declined to be renamed party president last month after 10 years in that post. His withdrawal rocked the Popular Democrats, leaving them leaderless even as the aged Munoz Marin returned to the field.

Hernandez Colon, relaxed in his luxurious penthouse apartment, said he had departed to write a book that will outline "a new thesis" on what a perfected commonwealth system must be.But he declined to describe his solution. "Puerto Rico is going through a crisis," he said. "The Carter people are not our friends . . . If there is support for this new thesis and if it appears that I am the best person to take the case forward, then I will be the [Popular Democratic] candidate in 1980."

He produced a thick computer printout of a poll done for the party by Peter D. Hart Research Assoiciates in Washington last May, in which 2,110 Puerto Ricans were interviewed on their political opinions. The $24,000 survey showed that 50 percent still favor commonwealth, 33 percent favor statehood and 6 percent prefer independence, figures Hernandez Colon said mean he could beat Romero in 1980.

To run, however, he will have to persuade the new party president, former Senate minority leader Miguel Hernandez Agosto, to keep a promise that he "will not be an obstacle" should the prodigal son return.

Hernandez Agosto repeated that promise to an interviewer, but he is ambitious to be the first non-blanquito , or member of the white upper-class family network, ever to be elected governor. He alone will speak for the party before the United Nations, he said; he was careful to associate himself with Munoz Marin's reappearance, and he comes as a relief to some in the party who disliked Hernandez Colon's discotheque-going style. Nationalists on the Left

WATCHING all this maneuvering with a jaundiced eye are the Puerto Rican Independence and Socialist parties, socialist and communist respectively, which confidently predit that the United Nations will brand Puerto Rico a U.S., colony next week and spur their hopes for a clean break. The last time the island voted exclusively on the status question, in 1967, the independents boycotted the event and got 0.6 percent of the vote, to statehood's 38.9 percent and commonwealth's 60.4 percent.

Independence party leader Ruben berrios pointed out, however, that only 700,000 persons voted then and that fully 1 millin more voters have since joined the rolls. Even the 1976 election results that gave the independents 6 percent do not reflect the full depth of nationalism here, he said, which would surface in any contest between "the true alternatives, statehood and independence."

"What we have obviously isn't working. Statehood is an impossible myth; Congress would be insane to grant it. There is no alternative but independence," Berrios said.

He and Socialist Party leader Juan Mari Bras both charged that they are continually harassed by the government and that on one has been arrested in connection with several bombings, apparently by the island's strong right wing, of their homes and offices. Mari Bras' son was killed in 1976. The murder suspect, he said, was declared mentally unfit for trial and nothing further has been done.

Both men predicted endless violence from "frustrated patriots" while the status question remains unresolved, and said no patriot would ever accept statehood. However, they each denounced the pro-independence terrorists of FALN, the U.S.-based National Armed Liberation Forces, who have claimed reponsibility for dozens of mainland bombings involving several deaths.

"The independence movement has been isolated from the rest of the world, but not anymore," Berrios said. "International pressure is growing . . . the question of status will have to be resolved in the next decade."

All sides would be likely to agree to that. The U.N. debate, according to Berrios, Romero and the three Popular Democratic leaders alike, will be their next opportunity to convince President Carter that the present situation cannot continue much longer.