The bomb went off during half time. The aerospace salesman was praising the Uruguayan goalkeeper and had stopped to sip his drink when down in the flat part of Lima there was a sudden great boom, the kind you can feel in your feet.

It would not be entirely fair to say nobody noticed. The aerospace salesman looked up and said, "Explosion," and everybody watched smoke billow for a minute or two, and then the hostess shouted from the television room that the soccer game was about to start again. In yesterday's papers it said the bomb blew out the iron garage door and most of the windows of the headquarters of Popular Action, the political party of the Peruvian president. The building guard was startled but unhurt; he had been sitting a safe distance away, transfixed before his television set, watching the game.

Mysterious extremist groups are blowing up Peruvian buildings and power stations, 7,000 public health doctors just went back to work after a month-long strike and miners, sanitation workers and bus drivers are still out on strike. If you picked up a Peruvian newspaper yesterday you would have to do some work to find any of this in print. In all Peru, there is only one story this week that really matters, and it is splashed over front pages in World War II-size headlines with full color photographs to match: "WITH SOUL, HEART, AND LIFE--PERU WON."

Actually, Peru did not win. The Peruvians could not seem to get a single shot past the extraordinarily quick Urguayan goalkeeper, so they tied, 0-0. But a tie was all they needed to eliminate Uruguay from the South American playoffs for soccer's World Cup in Spain next summer. For the fourth time in its history, Peru is going to the World Cup--or as it is more properly known by the millions of South Americans who hang anxiously on its every development, the Mundial.

The Mundial, which a lot of North Americans fit dimly into that category of suspect foreign things like soccer and the metric system, is the most important international event of the Spanish-speaking world. It pits 24 teams against each other in a game in which Latin Americans excel. It reaches more people and stirs far more passion than economic pacts, mutual defensive arrangements, border wars, oil price negotiations, coup d'etats and all the other significant affairs of state about which important people busy themselves.

EVERY NEIGHBORHOOD soccer game, every boy growing up trying to be Pele, every political regime eager for self-vindication, every grandstand fight and inter-city rivalry and slight to national honor--all of it bursts forth every four years, in the Mundial.

Argentines still get misty when they talk about their 1978 World Cup victory, which came in the midst of international accusations about the country's violent political repression.

Peru's 1970 qualification for the World Cup came shortly after the then-president, Gen. Juan Velasco Alvarado, nationalized a major U.S. oil company, and Velasco is reported to have cried, "This victory has the taste of petroleum!"

When you see men clustered around a store window in Bogota or Sao Paolo, you know that a soccer game is showing on a television inside. When Uruguay beat Brazil last January in the Gold Cup of soccer, which was played in the Uruguayan capital of Montevideo, the three-hour soccer-induced urban paralysis spread as far north as Caracas.

You can climb into a taxicab in northern Ecuador and ask the driver what he thinks of Diego Maradona, and he will know instantly that you are talking about a Buenos Aires soccer forward who is by now the most famous Argentine in the world.

In Lima you could feel the frenzy mounting three days before the game got under way. Letter From Peru Restaurant waiters stared at wall-mounted television sets, their customers forgotten, as commentators weighed Peru's chances. The editor of the news magazine Caretas tried valiantly to consider something else to put on the magazine cover in the unthinkable event that Peru lost. (The winning cover said simply, "We Made It.")

BY SUNDAY AFTERNOON, it was fairly evident that the only people in Lima not paying attention to the game were the dynamite throwers outside the Popular Action headquarters--and they, it must be noted, waited until the end of the first half. In hospitals, patients wrapped themselves up in white gowns and clustered around the central television sets. People too poor to own televisions crowded into the nearest restaurants and bars. A young man fell 60 feet from the top of the stadium because he had climbed up the night before to get a good seat and had fallen asleep; he escaped with a broken leg, and one can only hope the hospital's television was working.

When it was over--when the players had fallen on their knees and crossed themselves and leapt all over one another the way Latin American soccer players do--the people of Lima took to the streets. La Prensa, a major morning daily, had a special four-page edition out 20 minutes after the close of the game, and you could see people clutching it worshipfully to their chests, or flattening it against their car windows as they drove by.

A dejected Uruguayan radio reporter called Lima yesterday morning to say, in his Uruguayan Spanish, that there was no joy in Mudville.

"Peru didn't even need a goalkeeper," he said. "If he had gone home Uruguay still wouldn't have made any goals. We'll have to watch one more Mundial from the back window, left out."

And Caretas editor Enrique Zileri, who staggered around his television in exhausted and giddy relief when the game was over, has his victory cover on the presses. He is a fierce defender of Peru's year-old democracy and figures he has his answer to the old petroleum cry of Velasco and his now-defunct military government. "I'm thinking of putting this on the story--'The Taste of Liberty,' " he said.