After 36 matches over two weeks, the 13th World Cup's preliminary phase confirmed what almost everyone has said all along: There is no clear-cut favorite to win soccer's most prestigious prize.

The first round produced no major upsets, few surprises and a frequently listless brand of soccer. With stadiums often half-empty, the people who stayed home looked all the wiser.

But now, in the single-elimination round of 16, the level and intensity of play can be expected to rise to World Cup standards.

"Now, the matches will be for life or death," said Bora Milutinovic, coach of Mexico's team.

The second round will begin Sunday with Mexico playing Bulgaria at Azteca Stadium here and the Soviet Union playing Belgium in Leon. The Mexicans, with a crowd of more than 110,000 expected, are heavily favored to beat Bulgaria, which still is without a victory after 15 matches covering five World Cup appearances.

There have been a number of interesting developments as the teams aim toward the June 29 final at Azteca:

*Brazil, the pre-Cup favorite, was the only team not to allow a goal in three first-round games, yet the three-time Cup champion did not make an overwhelming impression. Coach Tele Santana started a younger lineup in the club's final preliminary match, and Edson, Alemao and Casagrande were censured for extracurricular violations. "This place is turning into a monastery," Casagrande said.

*Morocco, the surprise winner of Group F, became the first African team in World Cup history to qualify for the second round. "For us, it is like winning the World Cup already. We should go home," said Morocco's coach, Jose Faria. Brazil's Socrates called Morocco's Mohammed Timoumi "one of the best players at this World Cup, the engine of the team."

*Denmark, in its first Cup appearance, has emerged as an engaging choice of many, joining Brazil as the only team to win all three of its first-round matches. Preben Elkjaer and Michael Laudrup lead the offense. Not everyone is a believer, however; Argentina's Diego Maradona was quoted as saying, "Denmark deserves the same respect as Iraq."

*West Germany, despite Coach Franz Beckenbauer's public declarations that the team is not championship caliber, must beat only Morocco and probably Mexico to reach the semifinals. Star Karl-Heinz Rummenigge, who has been slowed by a leg injury, said, "Some players are against me on this team," and he recently met with three teammates from the West German league's Cologne club to square away differences.

*Mexico, trying to become the sixth host nation to win the Cup title, continues to play down dissension between star Hugo Sanchez and teammates. Milutinovic said the team deserves more credit than it is given: "You only mention Hugo Sanchez, when the whole team is worth mentioning."

With the exception of Morocco, the round-robin group winners -- Argentina, Mexico, the Soviet Union, Brazil and Denmark -- are considered strong contenders to make the final. Second-place finishers that bear watching are Italy, France, West Germany and Spain.

But for either Italy or France, the competition will end Tuesday when they meet at Olympic Stadium. Italy's coach, Enzo Bearzot, who is often coy with reporters, said: "We have to prepare accordingly. Of course, we have to score, too."

Once again, media reports have speculated that Bearzot may activate striker Paolo Rossi, the 1982 World Cup star who has yet to play here for the defending champions. If activated, Rossi almost certainly would be a reserve.

If any team seems a sure shot to gain the semifinals, it is Argentina. To make the final four, the Argentines must beat Uruguay and then the England-Paraguay winner. Those three potential opponents scored a combined nine goals in nine first-round matches.

The Argentines have acclimated themselves to the Mexican heat and high altitude. They have offensive balance, experience, an underrated defense and a level-headed coach in Carlos Bilardo.

Most importantly, they have Maradona.

The incomparable Maradona has scored or assisted on five of Argentina's six goals, and he, more than any other player here, seems capable of carrying his team to the top.

"Argentina steps on the accelerator whenever it wishes to," Bilardo said. "We respect our opponents, but we don't worry about them or make changes geared to them. We worry about our own game, and our game is a solid one."