UPDATE 4-Brazil blackout blamed on storm, grid in spotlight

* Power restored after huge blackout hits Sao Paulo, Rio

* Government says storm short-circuited transmission lines

* Doubts over Brazil infrastructure despite economic rise (Recasts with cause of blackout, adds quotes)

By Eduardo Simoes

SAO PAULO, Nov 11 (Reuters) - Brazil's government blamed a severe storm for the power outage that put the country's economic heartland in the dark for more than five hours and raised doubts about the reliability of its energy grid.

Tuesday night's blackout, Brazil's worst in a decade, left tens of millions of people without power across most of the wealthy southeastern region, halting subways and snarling traffic in major cities like Sao Paulo and Rio de Janeiro.

A combination of lightning, rain and heavy winds caused three transmission lines to short-circuit in Sao Paulo state, setting off a ripple effect that forced the massive Itaipu hydroelectric plant on the border with Paraguay to shut down automatically, Energy Minister Edison Lobao said on Wednesday.

"Our grid is strong and resistant but there are moments that the system simply can't withstand," Lobao told a news conference in the capital Brasilia, stressing that weather-related blackouts are commonplace around the world.

Responding to criticism the government has neglected to maintain and upgrade Brazil's energy infrastructure, President Luiz Inacio Lula da Silva said investment in transmission lines over the last seven years amounted to 30 percent of what had been spent over the preceding 120 years.