The countdown to the 12th soccer World Cup, the non-American sports world's World Series, has ended, with about six teams given a realistic chance of winning the tournament that begins today in Barcelona with a game between defending champion Argentina and Belgium.

The 24 teams are divided into six groups of four teams each. Two teams from each group advance to the second round, of four groups of three teams. The first two rounds will be round robins, and the four survivors of the second round will be paired to determine the July 11 finalists.

Here is a breakdown of the groups and each team's prospects: Group One

Italy is the favorite in this group, but will have to improve considerably on recent performances to avoid being knocked out before the second round. The Italians will field a veteran team, led by 40-year-old goalkeeper Dino Zoff and defenders Claudio Gentile and Gaetano Scirea. For the past decade, Italian soccer has cultivated a reputation as being dull and defensive-oriented.

Several questions remain about Italy's offense: how badly out of form will goal-scorer Paolo Rossi be after a two-year suspension for his alleged role in a bribery scandal? Can playmaker Giancarlo Antognoni shake off the effects of a skull fracture suffered several months ago?

Poland finished third in the 1974 World Cup and was in the final eight in 1978, but does not appear as strong this year. One of the Polish team's strongest players is Zbigniew Boniek, 26, who will be playing in Italy next fall. Many of his teammates are likely to be highly motivated, hoping for an opportunity to leave Poland for rich teams in Western Europe.

Peru is in the World Cup final rounds for the third time in the last four tournaments, and is a serious threat to advance to the second round ahead of Poland and Italy. One star of the 1970 and 1978 Peruvian teams, Teofilo Cubillas--of the North American Soccer League's Fort Lauderdale Strikers--is back, but he may play a secondary role behind a new superstar, Julio Cesar Uribe, 24, a clever midfielder. Peru's problems may be the opposite of Italy's: the offense is strong, but the defense is a bit suspect.

Cameroon is unlikely to win a game, but has a cadre of flashy attackers. The team suffers, however, from a lack of discipline. Group Two

West Germany, which won the World Cup in 1974 but was eliminated in 1978, is the clear favorite in this group and, along with Brazil and Argentina, a title favorite. The Germans easily won all qualifying games and are strong at all positions. They will rely on midfielder Paul Breitner, a veteran of the 1974 team, and attacker Karl-Heinz Rummenigge, two-time European player of the year, for offense.

To show how strong the Germans can be defensively, young Lothar Matthaeus shut out two of the world's top stars, Brazil's Zico and Argentina's Diego Maradona, on a recent South American trip--and Matthaeus hasn't even won a starting job yet.

Austria would like to duplicate its 1978 World Cup upset of the Germans, but that does not seem likely. As in 1978, the Austrians will look to Hans Krankl and Walter Schachner to provide scoring and goalkeeper Friedl Koncilia and world-class sweeper Bruno Pezzey to anchor the defense.

Chile is considered the weakest of the four South American teams in the finals, although the Chileans may challenge Austria for second place in the group. Their hopes revolve around Elias Figueroa, 35, (former Fort Lauderdale teammate of Cubillas) and Carlos Caszely, 31, both of whom played for Chile's weak 1974 World Cup team in West Germany.

Algeria may be the best of the non-European, non-South American clubs in the tournament, but it would be overly optimistic to expect it to make the second round. Group Three

Argentina has struggled a bit in recent test matches, but the defending champion generally fields a lineup with nine starters back from the 1978 team. That lineup includes tournament star Mario Kempes, plus two young superstars: Maradona and Ramon Diaz.

Belgium and Hungary are capable of upsetting Argentina if they have a good day. Belgium relies on a physical defense and Hungary on a fluid attacking game.

The Belgians had hoped to boost their offense by naturalizing former Washington Diplomat Juan Jose Lozano, who has had two superb seasons for Anderlecht after a mediocre, injury-ridden year in the NASL. But the application was rejected. Belgium will call on its savvy captain, Wilfried van Moer, 37, to provide leadership and 23-year-old Erwin Vandenbergh to provide goals.

The Hungarians return many holdovers from their promising but disappointing 1978 team, led by Tibor Nyilasi and Andras Torocsik. They could be a pleasant surprise.

El Salvador will be out of the running. Group Four

England was not expected to be a big favorite this year, but has shown exceptionally good form in the last six weeks and could be the dark horse, along with the Soviet Union. The English are led by Southampton's Kevin Keegan, who has just begun to regain the form that made him Europe's top player in 1978 and 1979. England also has two of the world's classiest goalkeepers in Ray Clemence of Tottenham Hotspurs and Peter Shilton of Nottingham Forest. Paul Mariner, Trevor Brooking and Trevor Francis give the English a lot of depth in their attack.

France has a fluid team with much individual talent, capable of beating anyone when it plays to its potential. France is directly responsible for the fact that the runner-up from the last two World Cups, the Netherlands, did not qualify. The French midfield is one of the world's strongest, including Michel Platini, Jean-Francois Larios and Jean Tigana.

Czechoslovakia is similarly attack-oriented. Its fortunes will rise and fall with the play of striker Zdenek Nehoda and midfielder Antonin Panenka. The Czechs could surprise and take this well-balanced group.

Kuwait cleaned up in the Asian qualifying zone, but is not expected to go too far in the tournament. Nevertheless, the players will be rewarded with handsome bonuses for every game they win. Best players: winger Faisal Dakhil and midfielders Said Houti and Mahboub Mubarak. Group Five

Spain was seeded first in this group, and since the host team has won three of the last four World Cups, must be considered one of the top contenders. Nevertheless, despite the success of Spanish club teams such as Barcelona and Real Madrid, the Spanish national team rarely has been a world-beater.

The team's heart is a group of players from the Real Sociedad team of San Sebastian in the Basque country. They include goalkeeper Luis Arconada, striker Jesus Satrustegui, winger Roberto Lopez Ufarte and midfielders Jesus Zamora and Miguel Alonso.

Yugoslavia would be one of the world's strongest teams except for one small problem: they traditionally have had problems scoring. How good the Yugoslavs will be depends on how well midfielder Vladimir Petrovic, 26, plays.

Northern Ireland is the weakest of the three British teams in the tournament, and it is unlikely that this collection of second- and third-division players--and two NASL players--makes it to the second round. The strong point of the team is world-class goalkeeper Pat Jennings of London's Arsenal club.

The fact that Honduras, which probably isn't as good as Northern Ireland, and El Salvador are the representatives of the northern part of the Western Hemisphere points out, unfortunately, just how badly North American soccer measures up on the international scene. Group Six

Brazil is considered by many the odds-on favorite to win its fourth World Cup. There was some fear that the Brazilians may have peaked a year early during a brillant European tour, much as West Germany did in South America a year before the 1978 finals. But the last two tuneups for Brazil, including a 7-0 rout of the Republic of Ireland, showed how dangerous this team is.

As in past years, Brazil relies on sudden, unexpected thrusts forward from the back line and fancy free-kick variations. They also have one of the world's flashiest forwards in Zico and the only physician playing in the cup, Dr. Socrates, the team captain.

The Soviet Union and Scotland are two more reasons that Group Six is considered perhaps the toughest of the six.

The Soviets, led by attackers Oleg Blokhine and Ramas Shengeliya and sweeper Alexander Shchivadze, have a legitimate chance at winning the title. But they have lost midfielder David Kipiani, perhaps their best player, to injuries, and this will slow their attack.

The Scots have been the hard-luck team of the last two World Cups. In 1974 they were the only unbeaten team eliminated in the first round, and in 1978 a careless tie against Iran caused them to be eliminated early on the basis of goal difference behind the Dutch. Scotland's top performers are Kenny Dalglish, Graeme Souness, Asa Hartford and Danny McGrain.

New Zealand is another team just happy to be in Spain. In fact, its main goal is to score a goal.