Italy's stunning upset Monday over Brazil, the odds-on favorite to win the 1982 World Cup, has thrown the competition wide open, with none of the four semifinalists emerging clearly as the team to beat.

Italy now must face Poland, a team with which it always has had difficulty, in Barcelona Thursday, and West Germany meets France in Sevilla.

Here is a look at soccer's final four: Italy

Based on their performance against Brazil, the Italians would appear to be the new favorite, but they will need another good game against Poland. The two teams played a scoreless tie in the first round in Vigo on June 14, and with any luck the Poles would have won.

Italy reached the second round on the basis of that game and two 1-1 ties, against Peru and Cameroon. They beat Argentina, 2-1, and Brazil, 3-2, in second-round action. With the exception of Monday's game against Brazil, the Italians relied on a tough, often brutal defense and a cautious offense based on a counterattacking strategy.

The key question is whether the Italians will take the initiative against the Poles, or whether they will revert to their old habits. The old habits are hard to break, and Poland has been a problem for Italy since the 1974 World Cup, when the third-place Poles eliminated Italy with a 2-1 victory in the first round. The two teams also played two scoreless ties in connection with the 1976 European Championships.

Finally, Dino Zoff, the 40-year-old goalkeeper and captain, had another excellent match against Brazil. He directed his team's defense, but also successfully admonished his teammates to continue their offensive style. He must continue to show that kind of leadership if Italy is to beat Poland. Poland

After two scintillating victories over Peru and Belgium by 5-1 and 3-0 scores, the Poles got cautious against the Soviet Union, and settled for their third goalless draw of the tournament. In the first round they also tied Italy and Cameroon.

Grzegorz Lato, a veteran of Poland's 1974 World Cup team when he led the tournament in scoring with seven goals, has been a key player on this year's team, and he will need to take on more of the load, since the team's superstar, Zbigniew Boniek must sit out a one-game suspension for drawing two yellow cards in the tournament.

Lato has been playing on the right wing, but has been as much in his team's midfield and even goes deep into the defense to help bring the ball forward.

Sweeper Wladyslaw Zmuda, the Polish captain, has been the steadying influence in a steady defense, and his long passes to both wings have helped open up the offense.

Poland has shown that it is capable of playing various styles of soccer and of adapting to different kinds of opponents. But the team is strongest when it puts everything into the attack. Matchups

Italian defender Claudio Gentile marked Argentine star Diego Maradona out of the first second-round game, and he would have been assigned to do the same to Boniek.

One of these two men will play a key role in the final, but not Thursday. Andrzej Szarmach, another veteran of Poland's 1974 team, may be asked to replace Boniek, and Giuseppe Bergomi probably will step into Italy's defensive alignment.

Fulvio Collovati or Bergomi will have to contain Lato, and goalkeeper Pawel Janas of Poland will have to contain Rossi, who is just getting back into prime form after a two-year absence from competitive soccer. West Germany

Jupp Derwall, the West German coach, couldn't bear to go to the Santiago Bernabeu Stadium to watch the match between Spain and England that decided his team's fate.

"I won't go," he said. "I can hardly stand the suspense. I'll probably just have a glass of beer somewhere or just take a walk, rather than even watch the game on television."

Derwall's attitude reflected the situation faced by the West German team. Seen as one of the three leading favorites, along with Brazil and Argentina, before the tournament, the Germans played poorly in the first round and not always convincingly in the second. They had to wait it out as two other teams decided their fate.

It was a moral lesson that is not likely to be lost on the high-paid pros from Munich, Hamburg and Cologne, since it was only on June 25 that they played a key game against Austria that decided the fate of little Algeria, which had beaten the Germans, 2-1, in one of the four or five greatest upsets in World Cup history.

The Austrians and West Germans were both highly criticized for their nonefforts after the Germans got the early goal they needed to advance. The Algerians were left out because the Austrians were unwilling to work for at least a tie and the Germans would not try to score at least three goals.

The Germans are now in a clear upward trend, and their 2-1 victory over Spain showed how dangerous they can be. They attacked constantly, and with a little luck the final score would have been much higher.

Two key performers against Spain were sweeper Uli Stielike, who plays for Real Madrid, and Paul Breitner, who used to.

Both men sparkled in Real's home stadium, with Stielike in particular doing everything. Another world-class performance against France and Stielike can lead his team into the final.

West Germany is solid in defense, with goalkeeper Toni Schumacher, Stielike, the Foerster brothers, Karl-Heinz and Bernd, and Hans-Peter Briegel, who went forward so much against Spain that his direct opposite had to worry more about him than vice versa.

Nominal defender Manfred Kaltz played in midfield against Spain, which probably confused the opposition, and Breitner directed the attack. Up front, Pierre Littbarski had another good game on the wing, and Klaus Fischer joined Littbarski as a goal-scorer.

The central personnel question for Derwall is whether his star forward, Karl-Heinz Rummenigge, will be fit enough to do any damage in the attack. Rummenigge, who has been suffering from a thigh injury since he scored a hat trick against Chile in the first round, was ineffective against Spain and had to be taken out. France

This is one of those teams capable on one day of winning, 5-0, and losing the next day by the same score. It is an incredibly moody team that played excellently Sunday in defeating Northern Ireland, 4-1.

In the first round, France started off well in its first game against England, only to collapse and lose, 3-1. It then dominated Kuwait, 4-1, but had problems with Czechoslovakia and had to settle for a 1-1 tie.

Before the Northern Ireland game, it opened the second round with a convincing, but uninspired, 1-0 victory against an Austrian team that appeared to have lost its snap.

Which France will play against Germany Thursday? Will it be the France with a midfield second to none, led by Michel Platini, supported by the ever-dangerous Alain Giresse, the elegant Jean Tigana and Bernard Genghini, a hard-working two-way player?

Will it be the France with one of the most dangerous wingers in the world in Dominique Rocheteau--or two of the most dangerous if it decides to go with a three-man front line with Didier Six? Or will it be the same team that stumbled against a second-rate Czechoslovak team and held back against Austria? Matchups

West Germany has the edge in goal with Schumacher being more consistent than Jean Luc Ettori, who only won the starting job a day or two before the cup began.

Defender Manuel Amoros may get the thankless job of trying to keep up with Littbarski, which would be to West Germany's advantage. If Briegel can keep Rocheteau as busy as he did his Spanish opponent, he may succeed in neutralizing the Frenchman somewhat.

The best direct matchup, and one that most appreciative fans would pay good money to see, will be Platini against Breitner. It is unlikely that both will try to directly defend against the other, but as each team's leading playmaker, they are bound to cross paths often.