The work, budgeted at 705.6 million reais ($398 million) started with the removal of the seats in the lower ring of the stands in the stadium, the likely venue for the final.
Renovations will see the stadium's capacity reduced by more than half to 45,000 for the next 50 days and then closed.
The work is scheduled to be completed by December 31, 2012, in time to stage the Confederations Cup in Rio the following year.
The changes to the stadium, the biggest in the world when it was built for the 1950 World Cup finals, include redesigning the lower ring, new access ramps, an increase in the roof over the stands and a reduction in the size of the pitch.
It is its second major refurbishment in recent years after being closed for almost a year before the 2007 Pan-American Games, a 130 million reais project that fell short of FIFA [ Images ] demands for the 2014 World Cup.