* Rousseff's approval rating drops to 31 pct from 55 pct
* Third poll to signal decline in her re-election chances
* Economy could further hit her popularity in future
An opinion poll released on Thursday cast fresh doubt on President Dilma Rousseff's re-election chances next year, showing that her approval rating plummeted following massive street protests that swept Brazil last month.
The share of Brazilians who consider Rousseff's administration "great" or "good" slumped to 31 percent from 55 percent in mid-June, putting it on par for the first time with those who disapprove of the government, according to the survey by polling firm Ibope.
The survey was the third major poll in recent weeks to show Rousseff's popularity plumbing new lows, a remarkable turn of events for a politician who just two months ago was one of the most popular democratically elected leaders in the world.
Taken together, the polls indicate that the unexpected outpouring of discontent that shook Brazil in June has dramatically changed the country's political landscape. For Rousseff, that appears to mean a much tougher run for re-election in 2014 as voters clamor for change.
The protests were sparked by outrage at an increase in bus and subway fares in some cities, but quickly transformed into a nationwide movement against poor public services, rising inflation, political corruption and a host of other complaints.
If those grievances were not enough, signs that Brazil's red-hot job market is starting to cool could mean yet another headache for Rousseff, whose administration is struggling to rekindle the economy and curb inflation at the same time.
The poll, commissioned by Brazil's National Confederation of Industries (CNI), showed that Brazilians are growing increasingly worried about the state of the economy, which has been stuck in a rut for nearly three years.
According to the poll, Brazilians believe fighting inflation should be one of the top priorities of the government. Improvements in healthcare and crime fighting are also considered top priorities.
"The recovery (of Rousseff's approval ratings) will depend a lot on how the economy evolves, on whether inflation continues to erode Brazilians' purchasing power" said Renato da Fonseca, a CNI official.
Rousseff, herself an economist, has pointed to record-low unemployment as one of the main successes of her administration after more than two years in office.
Although unemployment in Brazil remains low at 6 percent, government officials worry that a sluggish economy and rising interest rates could trigger more firings in coming months.
Rousseff has struggled to jump-start an economy that boomed in the previous decade under her predecessor and political mentor, Luiz Inacio Lula da Silva.
The Ibope poll also showed that, for the first time, most Brazilians consider her government worse than Lula's.
One of her possible rivals in next year's presidential election, Pernambuco state governor Eduardo Campos, enjoys the highest approval rating among 11 governors, the poll showed.
The Ibope poll, which was conducted between July 9 and 12, interviewed 7,686 people and has a margin of error of plus or minus 2 percentage points.