With less than six weeks left before the U.N. Summit on Sustainable Development, scheduled to kick off on June 20, many would-be visitors are complaining that they are finding scarce vacancies and exorbitant prices for the few rooms they do manage to track down.

Recent research by Reuters suggests rooms are listing for at least five times the normal rate the following week.

Despite its lush setting, popular beaches, and renowned nightlife, Rio is infamous for its aged, costly and scarce hotel rooms.

The problems cause frequent frustration for business travellers in a city with growing oil and financial industries. and are prompting many critics to worry about Rio's capacity ahead of much bigger events - namely the World Cup of soccer in 2014 and the Olympic Games in 2016.

The upcoming U.N. gathering, informally known as Rio + 20 because of the two-decade anniversary of the landmark Earth Summit in the city in 1992, is expected to draw more than 50,000 participants.

To prepare for the crush of government delegations from around the world, Brazil's government months ago reserved as much as 80 percent of the city's hotel stock. But the blanket reservation created a virtual block on available rooms for visitors from non-governmental groups, demonstrators, and others who hope to attend.

"We're worried," said Antonio Patriota, Brazil's foreign minister, in comments to reporters after a Senate hearing on preparations for the summit. "We want Rio + 20 to be inclusive, but the prices are very high."

Even some official delegations have been put off by the steep rates. The European Parliament, for instance, recently said it had slashed its delegation from 11 people to one.

"The absence of the European Parliament or other authorities will be harmful," said Luiz Henrique da Silveira, a senator from the southern state of Santa Catarina. At his bidding, the Senate approved an official request to Rio Mayor Eduardo Paes, asking him to negotiate with hotel owners or help subsidize the cost of rooms from municipal coffers.

By late Thursday, the mayor's office had not yet received the request.

COSTLY NIGHT IN COPACABANA

A online search Thursday for rooms in the city found only one of 135 listed properties - a hotel far from Rio's most popular and convenient districts - with vacancy during the event. A search last week yielded one available room in the popular Copacabana neighbourhood, advertising a nightly rate of 2,263 reais during the summit, compared with only 431 reais a week later.

Rio's local hotel association said occupancy during the period is expected to surpass 95 percent.

Even with the high prices and confirmed absence of several notable world leaders, including U.S. President Barack Obama, Patriota said the government has received assurances that most of the official delegations would attend.

François Hollande, France's president-elect, and Russian President Vladimir Putin confirmed on Thursday they will attend, Brazil's government said.

(Reporting by Maria Carolina Marcello in Brasília, Additional reporting by Pedro Fonseca in Rio de Janeiro, Writing by Paulo Prada, Editing by Jan Paschal)

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