COPENHAGEN -- When Rio de Janeiro was elected host city for the 2016 Olympic Games yesterday, the room where its bid team gathered turned into a boisterous party, with members in uniform navy or moss green blazers hugging, dancing, crying and waving Brazilian flags. The bid leader, Carlos Arthur Nuzman, yelled, "We did it! We did it!"

Rio and Chicago had gone into the day considered the favorites, touted ahead of Tokyo and Madrid. But by the time Rio was chosen by the International Olympic Committee to become the first South American city to host the Olympics, the Chicago delegation and its star-studded supporters were nowhere in sight. They had already left the building.

Despite the support of President Barack Obama, who flew in specifically to address the IOC voters, Chicago finished last -- out of the running in the first round of voting, with a paltry 18 of a total 94 votes. Tokyo received 22, with Rio getting 26, and Madrid, 28.

In each round, until one city gains a majority, the low vote-getter is eliminated. After Chicago was tossed aside, nearly all of its votes went straight to Rio in the second round. In the third, after Tokyo was eliminated, Rio won handily, 66-32.

The chance to bring the Olympics to an area that had never hosted the Games worked in Rio's favor. During its presentation, the bid team showed a graphic of the world and marked all the places that have held an Olympics. South America was glaringly bare. "There was absolutely no flaw in the bid," IOC President Jacques Rogge said.

Chicago officials had worked nearly four years and spent nearly $50 million to bring a Summer Olympics to the United States for the first time since the 1996 Atlanta Games. There were many possible explanations for Chicago's spectacular failure, but little consensus.

Some pointed to the regional block voting in the treacherous first round. Others said some voters, assuming that Chicago was a lock to advance because of the presence of Mr. Obama and his wife, Michelle, might have taken their early votes elsewhere. Many also blamed the rocky relationship between the U.S. Olympic Committee and the IOC.

Others said there was no explaining it. "Everybody was shocked at that result," said Rene Fasel, a Swiss IOC member, regarding Chicago's first-round ouster. "Everybody expected Chicago and Rio -- everybody. It was really strange, and I feel really sorry. If it would have been Chicago and Rio in the end, it would have been much closer."

Anita DeFrantz, one of two American IOC members, said she could not believe how the vote unfolded, particularly after the Obamas' visit. "I hate the fact that these elegant people were here, and then our country got treated that way," she said.

Beyond showing an apparent indifference to the United States' star power, the IOC vote was interpreted as a repudiation of the USOC, which has been in upheaval over the past year and has struggled to gain a favorable standing within the IOC.

"It was a defeat for the USOC, not for Chicago," said Denis Oswald, another Swiss IOC member. He said 10 to 15 fellow IOC members had approached him recently, wanting to discuss issues related to the USOC. He said a USOC leadership change "has not helped" either, and that it was clear that the Chicago bid and the USOC were not united.

Acting USOC Chief Executive Stephanie Streeter and committee Chairman Larry Probst have taken their posts in the last year, and have run into problems with the IOC -- most notably over their stalled plan for an Olympic television network and their share of the network and corporate sponsorship contracts.

"The United States, within the Olympic movement, hasn't engaged as well as we could have for a long time," said Robert Ctvrtlik, the USOC vice president for international relations. "There's a lot of politics going on. This isn't just on the merits. I don't think it's anti-American. Maybe we still don't have the horsepower to do some of the politicking within the movement."

For the first time ever, an American president met with the IOC on behalf of a U.S. bid -- which USOC officials called the country's strongest bid ever -- but that was not enough. This followed New York City's bid loss for the 2012 Summer Games, a second-round exit after winning only 19 votes.

"All we know is that the first round is always the most dangerous, and obviously we didn't have a large region of support," said Chicago's bid leader, Patrick G. Ryan. "We wanted to bring home the victory, and we didn't. It wasn't our day."

On his flight back to Washington yesterday, Mr. Obama was "disappointed" about Chicago's finish, but did not regret making the trip to push the city's bid. "I have no doubt that it was the strongest bid possible, and I'm proud that I was able to come in and help make that case in person," he said after arriving back in Washington.

In Rio, officials declared a holiday for city and state employees. While tens of thousands of people had begun the celebration on the city's Copacabana beach, where people dressed in shorts and bikinis jumped to samba music, the scene was different earlier in Chicago. All over the city, people responded to the city's elimination with astonished silence, blank looks and questions.

The word there had been that Chicago would survive at least until a late round of voting, if not win. Planned celebrations at schools, parks and restaurants ended abruptly yesterday morning, long before anyone had expected a verdict.

Geography was Rio's strongest point. It helped the city overcome concerns about security in the Brazilian city. There were also concerns that the country would be overextended because it is hosting the 2014 World Cup.

It helped Rio that the IOC has a history of trying to affect change with its choices for Olympic bid cities. The committee awarded the 2008 Summer Games to Beijing, hoping to help open China to the world. In 1988, it gave the Summer Games to Seoul to help usher in a civilian government. By choosing Rio, it could help the country develop faster and could bring an entire continent of people closer to the Olympic movement.

"Today is the most emotional day in my life, the most exciting day of my life," Brazil President Luiz Inacio Lula da Silva said.

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