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By Eduardo Simoes
SAO PAULO (Reuters) - Brazil's president denied on Wednesday that underinvestment was to blame for the worst power outage in a decade, which left a huge swath of the country in the dark for more than five hours and raised doubts about the reliability of its energy infrastructure.
The blackout on Tuesday night left tens of millions of people without power across most of the country's wealthy southeastern region, halting subways and snarling traffic in major cities like Sao Paulo and Rio de Janeiro.
President Luiz Inacio Lula da Silva summoned his energy minister, Edison Lobao, for an urgent meeting in the capital Brasilia on Wednesday to explain what triggered the outage.
Energy officials said it was likely caused when a storm downed three transmission lines carrying power from the giant Itaipu hydroelectric dam on Brazil's border with Paraguay, which supplies about 20 percent of Brazil's energy and 90 percent of Paraguay's.
"We didn't have a failure in the generation of energy, we had a problem in the transmission line," Lula told reporters in Brasilia.
He said his government had invested over the past seven years 30 percent as much in transmission lines as had been invested over the 120 preceding years.
Brazil's economy has forged ahead in recent years under former union leader Lula and was quick to shrug off the global financial crisis. But transport and energy infrastructure remain weak points for the country that will host the World Cup in 2014 and the Olympic Games two years later.
"The very long transmission lines in Brazil are very badly maintained," said Adriano Pires, director of the Brazilian Centre for Infrastructure Studies, adding that the blackout was unlikely to have been caused by bad weather.
"This shows that Brazil is very vulnerable. You can't leave a country the size of Brazil hostage to accidents," he added.
An energy ministry official told Reuters the outage was triggered because the system was not equipped to cope with three lines being downed.
"The system is designed to withstand two contingencies ... here we had three," said Marcio Zimmermann, the ministry's executive secretary.
Zimmermann denied that the problem could have been caused by computer hackers. U.S. television network CBS reported in its "60 Minutes" program this month that blackouts in Brazil in 2005 and 2007 may have been caused by "cyber attacks," quoting mostly unnamed U.S. intelligence sources.
The massive power failure was already being politicized on daily talk shows throughout Brazil, with opposition politicians accusing the government of negligence in maintaining the country's transmission lines.
The blackout on Tuesday affected 18 of Brazil's 26 states, including the capital Brasilia, and left all of Paraguay in the dark for about 15 minutes. Paraguay's state electricity company said that the problem originated in Brazilian power lines.
The last time Brazil suffered an outage on such a large scale was 1999, when a lightening bolt struck a transmission line in Sao Paulo state.
Power was fully restored in Sao Paulo, Brazil's bustling financial capital and South America's largest city, before dawn on Wednesday.
Traffic on the streets of Sao Paulo descended into chaos shortly after the power outage. Thousands of passengers were forced to exit stalled subway trains and walk along the tracks to get back to stations and make their way to the surface.
The city's streets were still clogged early on Wednesday after the mayor cancelled restrictions on the amount of cars allowed to circulate during rush-hour traffic.
In Rio, the beachside city that will host the 2014 World Cup and the 2016 Olympics, many tourists left their hotel rooms along Copacabana beach because of the lack of air-conditioning and milled around on the darkened streets.
(Additional reporting by Denise Luna and Rodrigo Viga Gaier in Rio de Janeiro and Daniela Desantis in Asuncion, writing by Stuart Grudgings, editing by Brian Ellsworth and Cynthia Osterman)