On the Viaducto, a six-lane freeway running east-west through the capital, traffic is nearly at a standstill and one lane in each direction is stopped completely. Car hoods are lifted and fans sit or stand on top of their vehicles, waving banners and chanting, "MEH-HE-CO! MEH-HE-CO!" A hard rain seems not to matter.

Vendors, on foot, stalk the freeway with noisemakers, flags and refreshments.

At every point of the route leading from Azteca Stadium, nearby residents gather on the shoulders of the road and on the median strip -- entire families watching the spectacle, picnicking and cheering on the passing vehicles.

This is World Cup soccer, a slice of the unparalleled fan involvement the sport commands. And this scene came after only Mexico's first match, a 2-1 victory over Belgium last week.

"When Mexico wins a World Cup match, the city stops for the day," said Aguilar Calderon, a concierge at a large hotel here. "If Mexico won the World Cup, the city would stop for a week."

"The World Cup is the greatest sporting event in the world today," said Jose Luis Roca, chairman of Spain's soccer federation. "There is the Olympics, of course, but the Olympics is more individuals than teams. The World Cup is team versus team, nation versus nation. There is more emotion generated by the World Cup."

Over most of the world, the World Cup stirs emotions that most U.S. fans cannot imagine.

The game of soccer is deeply rooted in European and Latin American cultures, and many nations' pride and identity are staked to the success or failure of their World Cup teams. The fans respond in demonstrative fashion: In 1966, after the Italian team suffered its most humiliating moment ever, losing to North Korea, 1-0, Italian fans waited until the early-morning hours to greet the players upon their airport arrival by throwing rotten vegetables at them.In 1970, Mexican fans in Guadalajara took such a dislike for England that many of them gathered outside the team's hotel the night before an important match against Brazil, honking car horns and singing until dawn to prevent the players from sleeping. England lost to Brazil, 1-0.In 1974, when Pele decided he no longer wanted to play for Brazil's national team, the case was taken to the Supreme Court in Rio de Janeiro. Chief Justice Perencha Martins ruled that Pele was not obliged to put on the yellow jersey and blue shorts to defend the honor of the nation on the soccer field, a decision that shocked many Brazilian fans.And in this 1986 Cup, after Uruguay was routed by Denmark, 6-1, Coach Omar Borras' family home was under guard after telephoned death threats.

At first glance, World Cup crowds have a lot in common with crowds at U.S. football games: the teen-agers trying to direct cars to private parking lots near the stadium, the myriad souvenir sellers, the tailgate parties before and after the contests, the "wave" making its way through each section.

But there's a lot more unseen baggage here.

FIFA, the international soccer federation, was founded in 1904. Soccer rivalries in Italy, England and West Germany go back much further than basketball or football rivalries in the United States. (In the English League, for instance, the newest stadium in use was built in 1923.)

In each country, the city-versus-city rivalries and regional tensions that build in national leagues surpass their U.S. counterparts. There are two major factors -- a longer tradition and a less transient society.

"The game is passed down, grandfather to father, father to son," said Roca. "Even though Europe is changing, the family in Valencia Spain remains in Valencia for generations, and the ties to the club there stay strong."

The rivalries go a step further when they expand beyond national lines. In Europe, the top club teams from each nation compete in the European Winner's Cup and the national teams compete in the European Nation's Cup. Then, of course, there is the World Cup.

"What you have is an intense pride in what your nation can do," said Michel Hidalgo, the former French national team coach. "In America, you have the Super Bowl, but then it ends. If all the world played American football, then the Dallas Cowboys could meet the best teams from elsewhere. Or the best U.S. compilation of football players could compete for a true world championship. Imagine that."

To sense the power of the World Cup, perhaps American fans can remember when the U.S. ice hockey team upset the Soviets at the 1980 Olympics. There was a surge of chauvinism, and it's that sort of puff-your-chest-out-and-show-the-world mentality that fuels the Cup's passion.

It is not always healthy passion. Fan violence in the United States is fairly limited; at European and Latin American soccer matches, it is commonplace. The Brussels tragedy of one year ago -- when English and Italian fans clashed, leading to 39 deaths as the stands collapsed -- drew worldwide attention to the problem.

"The violence is a symptom of societal problems, not soccer problems," said Phillippe Girard, a Belgian journalist and psychologist who is writing a book on the spectacle of the World Cup. "In Belgium and France, there are relatively few problems. But in much of Latin America, in Britain and Italy, where the gaps between rich and poor are growing, there are more problems. Soccer is a poor-man's game as much as any sport, and a lot of unhappy people are rebelling against their surroundings."

In some cases, fans threaten the safety of players. At the World Cup, the teams sit under protective coverings to shield them from thrown objects. Many league matches in Europe and Latin America have ended with fans going after visiting players or the referee and linesmen.

In other cases, the fans are merely sidelights. For instance, there is a sizable Argentine contingent here. These blue-and-white clad people wear bedsheets, unusual headgear and face paint, making RFK Stadium's Hogs look civil. A band of about 80 of them plays drums and horns all match long. During each half of play, these fans never sit down and never stop singing, all the more impressive in the hot afternoon sun.

Washingtonians may remember pictures of Georgetown the night the Redskins won Super Bowl XVII: a crush of humanity, with human gridlock at Wisconsin Avenue and M Street and scores of people climbing atop light poles and buildings.

Similar celebrations, although not quite as big, take place routinely on Sundays during the Italian League regular season. When Roma beats Napoli, thousands of Romans take to their cars and jam the streets for hours. When the stakes climb to events such as the European championships or the World Cup, the spectacle easily eclipses a Super Bowl party. Success at this level can shape the national psyche for a long while, bringing an infectious, sustaining sense of pride and patriotism.

"If you think of some of the countries that have been kicked around recently because of bad economies or armed conflicts -- Mexico or Iraq come immediately to mind -- can you understand the lift a World Cup title would give their people?" Girard said.

Former British prime minister Harold Wilson often said that he rode England's 1966 World Cup victory to reelection, with the soccer triumph creating a jubilant national mood.

Here in Mexico City, already there have been raucous street celebrations in which public monuments were defaced. Mexican officials fear what future victories might bring, but they even fear more the possibilities of an ugly scene should the Mexican team lose in an embarrassing or controversial manner.

In Italy, a half-hour before the Italy-Argentina match last week, traffic in Rome was snarled as people tried to get to their TV sets at home in time.

In Brazil, two first-round victories set off nightlong demonstrations throughout Rio de Janeiro, and many businesses opened several hours late the morning after.

In Spain, one of the state-owned TV networks featured a six-hour wrapup the day after the team's 2-1 victory over Northern Ireland.

"There is soccer, and then there is everything else," said Carlos Alberto, captain of Brazil's 1970 World Cup-champion team. "Every little boy, whether he lives in the city or the country, knows the names of all the players on the national team. Every man can give you an opinion on who is the best and who is not.

"In soccer, the smallest nation, such as Uruguay, can beat the largest nations," Alberto said. "When Uruguay beat Brazil in 1950, that remains a source of pride in Uruguay until this very day."

Incidentally, when Uruguay beat Brazil in the World Cup final July 16, 1950, in Rio de Janeiro, the game drew the largest Cup crowd ever -- 199,850.