If the torrential island rains of summer will relent, and the terrorist threats and acts of all seasons will abate, the eighth Pan American Games may begin here Sunday in relative harmony.

That, it appears, is a great deal to ask.

For two months, while Puerto Rico has labored to distinguish itself on a hemispheric stage as a dignified and competent host, the skies of this Caribbean isle have wept constantly.

Those who have spent five years preparing this two-week spectacular -- with more than 4,000 athletes from 34 countries in the Americas -- hope desperately that it is not an omen of tears to come.

Like Puerto Rico itself, these pre-Olympic games -- a testing and experimenting ground for the XXII Olympiad in Moscow in 1980 -- have two faces.

Outwardly, this town is a devoted host. The major highways of San Juan are decorated with a vast murals that represent all 22 sports to be contested here from track and field, boxing and swimming to roller skating, softball and archery.

The Pan American Village, though it might pass for a colorfully painted sweaty high-rise project in a stateside slum, nevertheless is a spirited meeting place of young soul-shaking athletes from half the world.

Amiability compensates for amenities.

The thousands of tourists, relatives of athletes and media folk who will jam the 35,000-seat Hiram Bithorn Stadium for Sunday's opening ceremonies are housed along the gaudy Condado strip with its beachside hotels, gambling casinos and air of Vegas-by-the-sea.

That is the sliver of reality that official Puerto Rico hopes to show the world for the first 15 days of July.

From the moment that Roberto Clemente Jr., 11, brings the Pan Am tourch into Bithorn and 5,000 pigeons are released, these games are intended to be a political and social showcase -- arguably the most conspicuous event in Puerto Rican history.

"We are determined to show our hemispheric brothers, through our actions and behavior, that Puerto Ricans are not hoodlums out of West Side Story,'" said the island's governor, Carlos Romero, in a telivision address this week. PAN AMERICAN, From E1>

Puerto ricans have been mistakenly stereotyped, said Romero, as given to alcoholism, drug addiction, gangsterism and laziness, as members of an oppressed U.S. colony.

After slaying these false conceptions, Romero, a majority of whose constituents are on public assistance from the U.S., flew to New York to discuss tariffs on Puerto Rican rum.

From the top floors of the athletic dorms, it is easy to see across a beautiful lagoon to the hovels and shanties of the squalid barrios which make Spanish Harlem seem a haven of refuge by comparison.

It is here that fear which surrounds these games is bred and fermented. This is Puerto Rico's hidden, and horrid, face.

As has become almost customary in major international competitions, this universe of politics and poverty, serious symbolism and blatant silliness, is determined to invade the periphery of sport.

On Friday, the Puerto Rican Socialist Party cut down eight American flags and managed to burn two in protests. Earlier that day, four men hurled a fire bomb at a National Guard headquarters [blowing up one garbage can], then had a shootout with military police in which no one was hurt.

"This is the start of terrorist acts by left-wing groups, for which we are prepared," announced the police.

Terroism long has been a Puerto Rican cottage industry -- argument still rages here about whether those who tried to assassinate President Truman in 1950 and the gang that shot up Congress in 1954 should be freed from U.S. prisons,

In fact, at least six island groups, four radical and two conservative, have been bragging about proposed disruptions.

They are being taken especially seriously since police busted a group called the Macheteros in late October and confiscated 288 sticks of dynamite, among other items.

Security at the Pan Am village is both excellent and oppressive to the point of being ridiculous.

"It's tighter than Montreal in '76" said one U.S. athlete, Dave Fellows. "You're virtually a prisoner within the village when you aren't competing. They won't even let taxis through the gates for fear of them having bombs underneath."

"I don't think there's going to be a whole lot of sight-seeing done by dudes wearing 'U.S.A.' jackets," said hurdler James Walker, captain of the U.S. track team.

"We haven't been given any specific instructions," said Walker, "but we've been told by our coaches to be on our best behavior, because Americans aren't exactly well-liked down here. I'm going to walk around smiling at everybody ."

Perplexing enough, the central touchy issues here seem like utter trivialities. Which flags will be raised over the stadium -- U.S. or Puerto Rican or both? Which anthem will be played? Which flies higher, which anthem is played first?

The chairman of the Puerto Rican Olympic Committee has resigned in disgust over just these protocol problems.

These games have many a red-letter day -- several of them the showdowns between th U.S., which has won 58 percent of all Pan Am gold medals, and militant Cuba, which has become the hemisphere's No. 2 athletic power, almost equaling the medal count of Canada and Mexico combined in the 1975 games.

However, just as dramatically awaited a day is the Fourth of July when all political issues here come to a head. The pro-statehood party, which is in power, wants to prove how worthy Puerto Rico is to become a 51st U.S. state.

The independence party, infuriated by dependence on Yankee dollars, wishes to show its disdain for gringos.

Once the gala opening of the First and the fireworks celebrations of the Fourth are past, perhaps Puerto Rico -- with its mobilized National Guard, its specially trained bomb squads, its fresh-off-the-assembly-line experts in hostage negotiations -- can stop playing its deadly serious version of the Keystone Kops.

Without question, the humid, cloying air of San Juan is full of an atmosphere of manic foolishness. "It is part of our temperament to make much ado about everything," said one Puerto Rican Pan-Am official. "No one knows what is going to happen, and almost everyone enjoys not knowing."

In an official pronouncement this week, the Romero government proclaimed, almost lightheartedly, "We are in imminent danger of serious disorders. . . . We anticipate the collapse of social structures and we are ready." Part of that radiness is 628 rookie policemen, just one week out of training school.

Gradually, the emphasis of these games should shift from debate about whether the U.S. Navy should practice its shelling on the off-shore isle of Vieques, to whether anyone can outbox Cuba's Teofilo Stephenson or outhurdle America's Skeets Nehemiah.

Then, although the 1980 Olympics are 54 weeks away, the true purpose of these games will come to the fore: partial glory now with the hope of an Olympic medal a year hence.

Many of the greatest amateur track stars, boxes weightlifters, swimmers,basketball and volleyball players in the world are gathered here.

For every modest disappointment, like the general scruffiness of the favored U.S. men's basketball team or the absence of many preeminent U.S. gymnasts, there is a bonanza like the U.S. women's basketball team [probably the greatest ever assembled] or Cuba's vaunted baseball nine [almost certainly the best outside the major leagues].

If the monsoons stop and the militants hold their fire, then this Olympics for the Western Hemisphere can justify the $60 million and the years of work which this determined, yet often denigrated island, has poured into its most abiding passion:sport.