Before the Games began Mexico heralded the Moscow Olympics as the apolitical "fiesta" of sportsmanship and good will.

The first few days of competition changed all that. For the moment, at least, the Soviets have garnered along with their medals a more negative image here than they have had in years.

Support for the Games first took a plunge during the diving competition. Mexican Carlos Giron seemed assured of a gold medal in the three-meter springboard competition when the leading Soviet diver mangled a 2 1/2 reverse somersault. But then the Soviet, claiming he was disturbed by crowd noise, was allowed a second chance and Giron had to settle for silver.

Then came Daniel Bautista, Mexico's favorite to win the 20-kilometer walk, seemingly striding his way to victory when suddenly -- at a moment when the television cameras were not on him -- he was disqualified for running.

Mexicans, who earlier were puzzled and incensed by the U.S. boycott, began wondering why they sent a team. They feel they were cheated, and the Games have not become, for many people here, a major political as well as sporting issue.

Margarita Michelena, writing in the leading daily Excelsior, claimed that "the simple Mexican, who knows nothing about politics has just received and assimilated a terrible message -- at last enciphered in his own code -- that has opened his eyes to the reality of Russian totalitarian aggression. . . . What has been done to our sportsmen (and others) is, essentially, what the government of the U.S.S.R. has done by invading, in turn, Hungary, Czechoslovakia and Afghanistan."

The reaction of Mexico is more intense than in the smaller countries of Central America, at least in part because victory hopes were so much higher here. Guatemala sent a team not so much in hopes of winning events as in an effort to show its independence from the United States.

Costa Rica's participation in the Games was the focus of considerable internal debate, heightened by a Soviet offer to pay the way of the Costa Rica's athletes. The offer was rejected, but the team went.

Nicaragua, which revived an intense sports program almost as soon as its revolution ended last year, pinned most of its hopes on its boxers. When one of the best was defeated in the early rounds of competition, few questions were raised about the validity of the decision.

Honduras was the only Central American nation that supported the boycott, but some Hondurans have been heard to complain that nobody outside the country seems to have noticed.

In Mexico, however, it will probably be some time before the furor dies down, and one of the principal focuses of anger is likely to become, finally, a Mexican who lost another sort of compeititon in Moscow. Mario Vazquez Rana, the head of the Mexican Olympic Committee, has been considered a likely successor to Lord Killanin as head of the international organization. He did not get the post, but his own political aspirations are now being blamed for leading Mexico into the Moscow mess.

"No one of good will," Michelena wrote, "or with any moral foundations, would send his children to a party held in a house of criminals. The games of youth? And a political, purely sporting event? Nuts."