As Iran's team prepares to step onto the field of the World Cup for only the second time since the Islamic Revolution of 1979, the soccer fever gripping the country reveals many of the pressures reshaping Iranian society. While Iran confronts the West over its nuclear program and its president promotes Holocaust denial, the country is also struggling with something far more fundamental: how to have fun together in public.

It is a challenge that has forced Iranians to try to sort through the intersecting strands of their identity, to confront decades of clerical rule that have emphasized traditions of mourning and to accommodate a population increasingly dominated by young people who are far more aware of the world beyond Iran.

"We do speak about this problem: how can we have a happy society?" said Behrouz Gharibpour, director of the main cultural center in Tehran. "We are in the center of trying to change, to find a good and accepted way to be happy — when we want to be happy."

Soccer, it turns out, has been one of the catalysts propelling that effort.

"As a people, we have this very sad streak in us," said Mansoureh Ettehadieh, a publisher and historian in Tehran. "Most of our music is sad. The Shia color is black."

But soccer, she said, has tapped into something else entirely.

"People need to go out and shout, to celebrate and to identify together," she said of the street parties that break out after victories on the soccer field, gatherings that would normally be broken up by Iran's Basiji morality squads.

Iran, long a powerhouse in Asian soccer, will play its first World Cup game on June 11, against Mexico. While Mexico is favored, Iran is considered skilled enough to pull off an upset — as it did in 1997, in a qualifying game against Australia, and in 1998 in a 2-1 victory over the United States — touching off wild celebrations in the streets.

The Iranian team is carrying a lot of responsibility, and baggage, to Germany. German officials have been under pressure to ban President Mahmoud Ahmadinejad because he has labeled the Holocaust a myth. But officials have said that under the rules of the soccer federation, FIFA, they cannot ban a head of state.

Mr. Ahmadinejad sidestepped the issue by delegating Iran's vice president, Mohammad Aliabadi, to attend. But even with the president staying away, the players themselves said they felt pressure to win as a way to confront the West in its bid to block Iran's nuclear program.

"There are pressures on our country, false propaganda, due to the nuclear program," said Muhammad Nosrate, a member of the team. "We want to prove who we are in sports."

Should Iran prove successful, even just in the first round, the police in Iran have already braced themselves for dancing in the streets.

"If they win, all of the people will express their emotions, 100 percent, and there will be no power to prevent them from doing this," said Ali Mudi, 44, as he sat in Laleh Park in Tehran. His friend Ahmed Maghail, 82, said he relished the idea of such a celebration: "All of the happiness and celebrations in my life were before 27 years ago."

Individually, Iranians know how to have fun. They are expert at shutting their doors and laughing in the privacy of their homes. But there are virtually no collective celebrations, nothing comparable to New Year's Eve in Times Square or the Rose Bowl extravaganza in Pasadena, Calif. And while young people have pressed for more cultural activities, like rock concerts or art shows, such gatherings are relatively few in number.

Since the Islamic Revolution and the rise of clerical rule, Iran's mullahs have restricted acts of public celebration, promoting instead acts of public mourning. For many people, rituals surrounding mourning have taken on the same role as cheerful activities in other societies.

In late May, in anticipation of the 17th anniversary of Ayatollah Ruhollah Khomeini's death, for example, Muhammad Salari and his family packed into a car and drove 16 hours from their home in Kerman, in central Iran, to the Khomeini shrine just outside Tehran. They pitched a tent on a small field in the middle of a parking lot and made a vacation of it.

"Let me put it this way," Mr. Salari said as he stood beside his tent. "It is a sad day, but we love this day."

Historians say that Persians have based their traditions on sadness and mourning at least since the adoption of Shiite Islam as the state religion in the 16th century. The most important Shiite holiday, Ashura, is centered on a monthlong mourning period to commemorate the death of Imam Hussein, the grandson of the Prophet Muhammad, who died in battle in 680. Even during Ramadan, when other Muslims celebrate after fasting all day, most festivities are banned here.

"It is a macabre mentality," said Ms. Ettehadieh, the historian. "Death is not celebrated, but it is taken very, very seriously. It is a sort of preoccupation of ours."

Iran's ruling clerics emphasize individuals who sacrificed their lives in the name of faith or country, while punishing outward displays of joy.

Drive through Tehran, and you will see buildings still decorated with huge murals of young men killed or maimed during the Iran-Iraq war in the 1980's.

Such ideas are pervasive and promoted by the government. In the ancient city of Bam, which has yet to fully recover from a devastating earthquake in 2003, a local cultural center wanted to have a music show to help cheer people up, but the government stopped it cold.

"Some people think that to help cure the depression among people in Bam they should come here and encourage music and dance," wrote Mohammad Ali Zareh, an education official. "This is a mistake. The problem will not be resolved this way and will only lead to the loss of the little faith that is left among the youth of this city."

But young people — and even many adults — are no longer buying into the culture of mourning. Even some of the most conservative Iranians seem to recognize that they need to rebrand Iranian-style Islam, to make it a bit happier. So in recent years they have begun to emphasize what are considered happy events, broadcasting videos celebrating the birth of religious figures. In a few locations in Tehran, officials even posted red banners — instead of black — to mark Ashura.

"Before, there was only crying and mourning," said Mr. Gharibpour, who also has produced operas. "Now television is showing they can be happy, you can distinguish between birth and death."

Iran's leaders were confronted with the problem when the soccer victories snuck up on them in the late 90's. Iran's team had last been in the World Cup in 1978, one year before the overthrow of the shah. And then came the triumphs over Australia and the United States.

The memory produces a breathless joy in many Iranians — and sends a chill up the backs of hard-line conservatives. The streets all over Iran went wild, with people dancing and women removing their head scarves in public, all as the wary morality police stood by powerless. Since then, soccer has become the property of the people — not the clerics — and with that there has become an unwritten rule allowing, or at least tolerating, collective joy in the face of a World Cup victory.

The Iranian government has recognized that, yet it has also tried to co-opt the celebration. Recently, for example, it honored the team members in a nonreligious ceremony featuring symbols of Iranian identity: a huge mural of the ancient city of Persepolis; hand-woven Persian rugs; and flowers, including roses, which are mentioned throughout the verse of the 14th century poet Hafez.

A few days later, the Iranians played Bosnia. With two huge portraits of Ayatollah Khomeini and Ayatollah Ali Khamenei staring down from the edge of the stadium, spectators bopped to the rhythm of Iranian rap.

"He's going to get the ball."

"And throw it on the field."

In Persian, it all rhymed, and felt almost as good as the final score: 5 to 2, Iran.