The Independence Party here need not worry, baseball has not Americanized Puerto Rico. Rather, it is the grand old gringo game that will never be the same.

What has this potential 51st state done to Senor Doubleday's sport? Transformed it from a stately pastime into something that Wrigley Field's bleacher bums could only dream of, that's what.

Any Yankee who has doubted in his heart that his countrymen had the requisite enthusiasm and passion for observation truly to appreciate their game, should take out applications to become an honorary Puerto Rican "beisbol fanatico."

One learns quickly - perhaps it is the free, introductory rum pina colada at the airport - that moderation in the pursuit of happiness is not the Puerto Rican way.

Automobile horns caterwaul in the parking lot of Hiram Bithorn Stadium. Cars are abandoned astride curbs. Thousands of people scurry across the plaza of cobblestones and palm trees, past the bronze statue of Bithorn, Puerto Rico's first big leaguer.

And that's just to get to batting practice on time.

This is the land where baseball may finally give mankind's big three of politics, religion and sex a run for their money.

"What I like here," says catcher John Wockenfuss, speaking for all the major leaguers playing winter ball, "is the rapid (sic) fans."

"They sure won't allow you to let down," says one Santurce player. "Even the laziest players hustle here. I once saw Sam McDowell knock himself out diving into a dugout for an overthrow. He came staggering back to our bench and said, 'I'm on vacation. Why the hell did I do that?'"

The tale is told here of an American League pitcher - known for using so many amphetamines that in defeat he would say, "I didn't get beaten. I just got outmilligrammed" - who always left his illegal "uppers" behind when he came to Puerto Rico.

"The fans are my greenies," he would say. "These people are leavin' earth. They need FAA clearance to get into the ball park."

It is customary for stadium guards to desert posts and leave gates wide open as soon as the first monumental cheer lures them inside to watch the game. And the first hit of the contest always gets a standing ovation.

A curve ball in the dirt, setting up the possibility of a walk, is enough to get the fans into full-scale debate.

Anyone who wants a cold drink and an empanidilla (deep-fried ground-beef-and-dough pie that is a Latin hot dog) can just wait until between innings. Vendors who block people's viston don't stay in business long.

The fans are roughest on native Puerto Rican players and any manager. "I won the winter league batting title his year partly to silence my people," says Sixto Lezcano of Caguas. "They think Puerto Rican major leaguers come back home not to play hard, to jake it."

"They've been booing managers for 40 years," says Caguas skipper Doc Edwards. "I understand Walter Alston and Sparky Anderson and Frank Robinson all got it. Why shouldn't I? There isn't one fan who isn't convinced he knows more baseball than I do."

The reason for much of the emotion here is obvious. "Most of the fans are poor working people," says Caguas reliever Roric Harrison. "They're got a tough life, a cruel one. This is where they can scream and yell and vent frustration."

Yet it is only in the midst of this panoply of emotion that baseball seemed as intense to the spectator as it has felt all along to those who are playing and managing.

Baseball only gives up its secrets to those who pay close attention. It is a game of anticipation and strategy, of long waits and crucial split seconds. Puerto Ricans relish the anticipation, argue the strategy incessantly, and go crazy during and after the vital plays.

And something can usually be done about the long waits. During a no-hitter this month two sides of the stands got into a paper clip battle.

Though rock- and bottle-throwing, those passions of some other sports-addled Latin nations, are rare here, harmless fistfights are an unfailing ritual entertainment.

"As soon as two guys draw back their fists, says Connie Lapore, baseball writer for the San Juan Star, "90 people jump in to separate 'em and the cops crawl all over the top of everybody."

Americans find it hard to believe this city of 700,000 can support three professional teams and that an island of 3.2 million can nourish six. But the fact is that pro baseball here is distinctly second fiddle to the amateur brand that rules the summer.

The government maintains 1,200 baseball fields and Puerto Rico's national amateur team is second in the world to Cuba. Across the street from Bithorn Stadium sits Roberto Clemente Coliseum, the island's academy of baseball, with nine constantly-used fields among its facilities.

Many is the mainlander who has come here to fish the tarpon-crowded seas and eat in the floating restaurants on Condado Lagoon.

But those who find their way to earthy Bithorn Stadium may discover something even more exotic - a new and exuberant game that vaguely resembles a sport they have seen before.

Then they, too, will be tempted henceforward to call themselves not baseball fans, but "baseball fanaticos."