* 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
By Alonso Soto
BRASILIA, July 25 (Reuters) - An opinion poll released onThursday cast fresh doubt on President Dilma Rousseff'sre-election chances next year, showing that her approval ratingplummeted following massive street protests that swept Brazillast month.
The share of Brazilians who consider Rousseff'sadministration "great" or "good" slumped to 31 percent from 55percent in mid-June, putting it on par for the first time withthose who disapprove of the government, according to the surveyby polling firm Ibope.
The survey was the third major poll in recent weeks to showRousseff's popularity plumbing new lows, a remarkable turn ofevents for a politician who just two months ago was one of themost popular democratically elected leaders in the world.
Taken together, the polls indicate that the unexpectedoutpouring of discontent that shook Brazil in June hasdramatically changed the country's political landscape. ForRousseff, that appears to mean a much tougher run forre-election in 2014 as voters clamor for change.
The protests were sparked by outrage at an increase in busand subway fares in some cities, but quickly transformed into anationwide movement against poor public services, risinginflation, political corruption and a host of other complaints.
If those grievances were not enough, signs that Brazil'sred-hot job market is starting to cool could mean yet anotherheadache for Rousseff, whose administration is struggling torekindle the economy and curb inflation at the same time.
The poll, commissioned by Brazil's National Confederation ofIndustries (CNI), showed that Brazilians are growingincreasingly worried about the state of the economy, which hasbeen stuck in a rut for nearly three years.
According to the poll, Brazilians believe fighting inflationshould be one of the top priorities of the government.Improvements in healthcare and crime fighting are alsoconsidered top priorities.
"The recovery (of Rousseff's approval ratings) will depend alot on how the economy evolves, on whether inflation continuesto erode Brazilians' purchasing power" said Renato da Fonseca, aCNI official.
Rousseff, herself an economist, has pointed to record-lowunemployment as one of the main successes of her administrationafter more than two years in office.
Although unemployment in Brazil remains low at 6 percent,government officials worry that a sluggish economy and risinginterest rates could trigger more firings in coming months.
Rousseff has struggled to jump-start an economy that boomedin the previous decade under her predecessor and politicalmentor, Luiz Inacio Lula da Silva.
The Ibope poll also showed that, for the first time, mostBrazilians consider her government worse than Lula's.
One of her possible rivals in next year's presidentialelection, Pernambuco state governor Eduardo Campos, enjoys thehighest 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 orminus 2 percentage points.