Mexicans partied in the streets and police manned barricades today after the national team qualified for the World Cup's second round with a 1-0 victory over Iraq, marking only the second time Mexico has survived the tournament's preliminary phase.

Many Mexicans, however, worry that today's celebrations will only increase the pressures that have been mounting on a team expected not just to win games but to lift the spirits of a nation battered by earthquakes, corruption scandals and economic collapse. Security officials, who have detained hundreds of often violent revelers following Mexican victories and ties, are preparing themselves for what they see as the inevitable day when the national team is beaten.

Concern about reaction to a Mexican defeat has been voiced at the highest levels of Mexico's government. "The day we lose, we will have our work cut out for us," a presidential aide said. "The pressures will be intense."

Experts in Mexican mass psychology disagree about the importance of the team's performance. "Soccer is a kind of war, and it tends to provoke violence everywhere, but Mexicans have been realistically expecting the team to be beaten sometime and are not likely to overreact," Fernando Cesarman, a psychiatrist, said.

But Antonio Santamaria, a psychoanalyst who has written frequently on the psychology of sports, warns that much of the Mexican public subconsciously sees the team's success as playing an important role in refurbishing Mexico's "international image and sense of identity."

World Cup fever "has unleashed a mania" in Mexicans, who are not usually serious soccer fans, agreed Alejandro Bulnes, a social psychologist.

If the Mexican team is eliminated, he said, "the letdown and disappointment will be terribly hard."

"Defeat will prick the balloon of Mexico's self-esteem," Bulnes said.

Some fans say the team's supporters aren't thinking about defeat, or about the criticism voiced by some that the players are being put under too much pressure. "We're not being too tough on them, no way. They have had plenty of time to prepare and do well," said Arturo Gomez, selling tacos from a makeshift stand across the street from Azteca Stadium.

"That's what the team is there for -- to do well or be criticized."

Mexican fans know well that the national team has had several factors in its favor -- the home field, longtime acclimation to the city's famously skewed ratio of pollutants to oxygen and membership in the weakest of the six groups of 24 national teams. The team also boasts what Mexico's coach has called "the most important player in the Cup so far" -- the deafening crowd support in Azteca Stadium, where 100,000 voices generate a roar like fighter jets scrambling in a hurricane.

Two days ago, as Mexico's coach was receiving local reporters after a morning practice, many Mexicans still were talking about their disappointment in the team's failure to defeat Paraguay Saturday, when star striker Hugo Sanchez had his last-minute penalty kick blocked, leaving the game tied, 1-1.

Sanchez, who had been cheered deliriously only minutes earlier, was excoriated by the departing crowd in savage chants, most of them at least slightly obscene. "The Sad Reality," read the headline in the sports section of "Excelsior," Mexico's leading newspaper, Sunday morning. Sportswriters also criticized Sanchez for drawing yellow cards in consecutive games, which kept him out of today's match with Iraq, and knocked the team for not pressing for victory.

"The game with Paraguay didn't have the euphoric, dramatic conclusion that the crowd wanted, but for us the results were better than the game," said the team's coach, Velibor Milutinovic, a low-key Yugoslavian who has spent 14 years in Mexico, first as a player and since 1975 as coach. "The important thing is to qualify for round two . . . and we have qualified."

Sanchez's missed penalty shot may have had a salutary effect on both the team and the public, Milutinovic said. "It showed Hugo's fans, and Hugo himself, that Hugo is human, and like every human being he can fail," the coach said.

Failure isn't what the fans expect, however, and with the team playing less than spectacularly, it has suffered unceasing criticism, much of it aimed at Sanchez and the affable Milutinovic, known here by his nickname, Bora.

"Listen, Bora," lectured a reporter for a prominent Mexican daily, "for a lot of us Mexicans it isn't enough to play to tie, to qualify. We want to see victories."

Milutinovic shrugged, and then smiled. "So do we," he said.

The fans' feelings have been obvious. Last week, after Mexico defeated Belgium, the team's supporters mobbed the Paseo de la Reforma, the capital's broad downtown throroughfare, blocking traffic, clambering up civic monuments and chanting victory slogans. By late evening, the festive spirit had turned sour, with vandals smashing windows and confrontations with riot police sending dozens to jail and more than 40 briefly to the hospital. On Saturday, following the tie with Paraguay, scores more of violent demonstraters were arrested.

Milutinovic said he has taken the advice of Octavio Rivas, a psychoanalyst who works here with the professional team "America," warning that the team must be shielded from the public's "unrealistic expectations."

"I tell them, like I tell reporters," Milutinovic said, "that this is a game, and the only thing that is expected of them is to make an effort for their flag."

Mexican fans poured into the streets today to celebrate the victory over Iraq -- motorists drove slowly along the Paseo de la Reforma beeping horns and the boulevard was filled with flag-waving paraders -- but the initial response was much more subdued than after the team's victory last week.