US President Barack Obama will make a whirlwind trip to Copenhagen this week to leverage his global popularity in a last-minute pitch for his hometown Chicago's 2016 Olympic bid.

The White House said Obama would arrive in Denmark on Friday, hours before the International Olympic Committee (IOC) votes on the destiny of the Summer Games after a final battle between Chicago, Madrid, Tokyo and Rio de Janeiro.

The trip represents a change of heart: the president had previously said the pressure of his under-fire health care reform drive would keep him at home, and nominated his wife, First Lady Michelle Obama to go instead.

But his reversal sets up a high-profile clash on the Olympian political stage between the US president and leaders from Spain, Japan and Brazil also expected in Denmark to push their nations' respective bids.

Michelle Obama will go to Copenhagen separately Wednesday, with Obama's longtime Chicago friend Valerie Jarrett, who now serves as a senior adviser and head of the White House office of Olympic, Paralympic and Youth Sport.

Both Obamas will make a presentation on their hometown as part of the Windy City's final pitch, the White House said.

"They will discuss why Chicago is best to host the 2016 Summer Games, and how the United States is eager to bring the world together to celebrate the ideals of the Olympic movement," the White House said in a statement.

High-profile backers of Chicago's bid, who had earlier said their chances would not be harmed by an Obama no-show, reacted with delight to his move.

"President Obama and First Lady Michelle Obama symbolise the hope, opportunity and inspiration that makes Chicago great," said Chicago Mayor Richard Daley.

"We are honoured to have two of our city's most accomplished residents leading our delegation in Copenhagen."

High-powered lobbying by government leaders and royals was seen as a major factor in swaying the IOC as it selected recent Olympic hosts -- London for the 2012 Summer Games and Sochi, Russia for the 2014 Winter Games.

London was awarded the 2012 Summer Games partly because former British prime minister Tony Blair went to Singapore to lobby.

Many existing venues and a compact geographical staging area are seen as the strengths of Chicago's bid, with Obama calling his home of nearly 25 years "a city of broad shoulders, big hearts and bold dreams."

Talk show star Oprah Winfrey will also lobby for Chicago.

In Denmark, the Obamas will meet Queen Margrethe and the president will also hold talks with Danish Prime Minister Lars Loekke Rasmussen, the White House said.

In Tokyo on Monday Japan's new Prime Minister Yukio Hatoyama said he will push Tokyo's bid at the IOC meeting.

"I want to do my best to help Tokyo host the Olympics," Hatoyama told reporters at his official residence. "In what ever game, we must win as a matter of course."

The Japanese capital plans to host what it calls the most compact, ecologically friendly and athletes-focused Olympics yet.

It has previously hosted the Summer Games, in 1964, an experience not shared by its rivals.

Spanish Prime Minister Jose Luis Rodriguez Zapatero said Madrid's bid faced difficulties but insisted that nothing was lost.

"It's difficult, but nothing has been decided because Madrid's bid is good, with great support and the most up-to-date infrastructure," Zapatero told radio Cadena SER.

However, "the fact that Latin America has never staged," the games could favour Rio, said the prime minister who was to travel to Copenhagen along with King Juan Carlos later this week to defend the Spanish capital's efforts.

Stephen Collinson
AFP