This excitable island knows how to party and it knows how to politic.

Both skills were displayed at maximum volume today as the VIII Pan American Games commenced with pomp and pigeons, music and mass marching, catcalls and cacophony.

Rain clouds finally rolled away, the sun shone and 35,000 fans in Hiram Bithorn Stadium kicked off these games with a hip-swinging, cheering and chanting afternoon of peaceful euphoria.

What was billed as a brisk "opening ceremony" turned into a fourhour spectacle of Caribbean Sunday Afternoon Fever. Puerto Rico could no more be ceremonious than fly.

Gov. Carlos Romero ringed this arena with troops and U.S. FBI agents to prevent threatened violent demonstrations.

No terrorists were in evidence. instead, 35,000 political activists were admitted with tickets. No such thing exists as a neutral Puerto Rican -- on any issue.

When the Star Spangled Banner was played, before the Puerto Rican anthem, the crowd drowned it out with a deafening eruption filled with air horns and police whistles -- the Latin American form of booing.

These people, traditionally commited to amplification, outdid themselves, producing a crescendo as painful as the starting-line thunder at the Indianapolis 500.

When the marrvelous card section in what was once the center field bleachers here, flashed the Puerto Rican flag [one star with stripes], the wall of noise changed from mixed cheers and jeers to pure applause.

As the Puerto Rican anthem, La Borinquena, was being sung, Gov. Romero, who ran on a statehood platform and who incurred wrath here for insisting on the presence of the U.S. anthem and flag at the Pam Am Games, suddenly began waving a Puerto Rican flag.

That started the whistles and horns again. It's difficut to try and play both sides of the street down here and pull it off.

The U.S. flag was scheduled to be raised at that point. Puerto Rico has been arguing about it for a year. Just when the throng was hot for some more Yankee Go Home fun, the agenda was switched and the American flag never was raised.

While the Star Spangled Banner was met with a combination of cheers, hoots, waving Puerto Rican flags and whistles, the 400 members of the United States team were universally cheered.

Only the enormous Puerto Rican squad, which must have dressed everyone on the island who tried out, was received more warmly than the U.S. gang with women's basketball star Ann Meyers carrying the flag.

The day's only subdued reception was for the powerful and haughty Cuban team in its all-white suits with Che Guevera-style red berets. Polite cheers, without any audible boos or whistles, greeted the Cubans, who unwrapped colorful dolls and threw them into the crowds as they took their turn circling the stadium.

Ironically, the crowd cheered enthusiastically for God Bless America, perhaps mistaking the Irving Berlin song for a local folk dance.

This was the day when Puerto Rico spread the peacock feathers of the national culture of which it is so proud and which is at the center of all its political turmoil.

In this atmosphere, where all parts of the political spectrum mix easily socially, it is consistent that constant threats of terror should be followed by no damage whatsoever.

"Puerto Rico has always had the most humanitarian terrorists in Latin America," said a journalist for the Marxist weekly Claridad. "They have always put their bombs where they will make the most noise and do the least damage. Of course, sometimes some one gets killed by accident."

On a day when politics was dominant -- with numerous anti-United States signs in the stands, the underlying motif was music, dancing and a tight-pink-short-shorts style of pulchritude.

In this competition, alas, the American women, through no fault of their own, finished a dowdy last.

To be sure, on Monday, when competition begins, the loudest early noises will probably came from the U.S. women's swimming team with its battery of such teen-age world-record holders as Tracy Caulkins, 16, and Cynthia Woodhead, 15.

But this afternoon the American women were camouflaged in baggy white midcalf dresses, Levi vests and clashing madras shirts. Latins covered their eyes in sympathy. A few American women had slit their skirts to midthigh in retaliation.

If the spectacular card section, which flashed running lions and hurdlers, and never missed on intricate designs like the Canadian maple leaf, was the day's technical highlight, then the muddy condition of the field was the downer.

Many contingents, including that of tiny Antigua whose seven athletes arrived after civil-war torn Nicaragua withdrew, had to march through 50 yards of over-the-shoe-tops mud. Precise formations crumbled as marcher after marcher, including Cuba flag bearer Teofilo Stevenson, gave that "Ugh-what-did-I-just-step-in" look and waddled awkwardly to high ground.

The first team to figure out what lay ahead and plan an alternate overland route was the U.S. squad.

In these Pan Am games, with so many pitfalls for individual athletes and for national athletic prestige, it was perhaps a sign that after today's lighting of the Olympic torch and releasing of 5,000 pigeons of peace, the United States would make other smart moves as well. CAPTION: Picture, Ann Meyers of women's basketball team carries the flag for United States contingent. AP; Chart, Official Calendar of the VIII Pan American Games, By Bethann Thornburgh for The Washington Post