By Peter Murphy and Carl Patchen

BRASILIA (Reuters) - Growing pessimism over Brazil's sluggish economic performance and rising inflation are starting to eat into President Dilma Rousseff's still-high popularity ratings, an opinion poll showed on Tuesday, the second in a week to show that trend.

About 54 percent of 2,000 Brazilians surveyed this month rated Rousseff's government as either "great" or "good," slipping from 57 percent in July 2012, according to the survey whose margin of error was 2.2 percent.

The poll was conducted by research company MDA Pesquisa on behalf of the National Confederation of Transport (CNT).

Brazilians are less optimistic that employment, income and public security levels will improve in the next six months and most expected health and education not to improve or worsen as the economy sputters after years of rapid growth, the survey said.

Two-thirds of respondents said inflation was having a moderate to high impact on their income as the government struggles to rein in price increases which recently hit the upper limit of its inflation target.

"It's inflation that is weighing most," Clesio Andrade, head of the CNT, said in a news conference in Brasilia on Tuesday. "People perceive rising prices and the impact on their income," he said.

Rousseff's personal approval rating slipped to 74 percent from 76 last year, with her still-high marks attributed to a tough stance on corruption and a close relationship with popular predecessor Luiz Inacio Lula da Silva, also from the PT or Workers' Party.

Rousseff, a trained economist and former left-wing guerrilla tortured and imprisoned during military rule, is widely expected to run in elections in late 2014. She would still be re-elected in the first round with 52.8 percent of votes if elections were held now, the poll showed.

While maintaining policies that have pulled millions out of poverty in the world's seventh-largest economy, Rousseff's government has struggled to tackle the underlying structural problems that are dogging economic growth and feeding inflation.

GDP grew just 0.9 percent in 2012 and a 0.6 percent in the first quarter of 2013, Brazil's statistics agency showed, while the export-led economy's trade surplus flipped to a $6.2 billion deficit in the first four months of 2013.

Last week, Standard & Poor's downgraded its outlook for Brazil's foreign currency debt rating to "negative" from "stable", citing deteriorating budget fundamentals and slow growth that could weaken the country's ability to pay its debt.

Rousseff's administration says the economy is beginning to pick up however, with private investment on the rise and falling debt to GDP levels. The government expects growth of around 3 percent this year while financial markets see a lower rate around 2.53 percent.

The CNT poll was similar to another by the Datafolha polling agency published on Saturday which showed 57 percent of Brazilians rated Rousseff's presidency "good" or "excellent," down from 65 percent in its prior poll.

The government's own private polls have also shown its popularity is slipping, chiefly due to concerns inflation is hitting people's spending power, local daily newspaper Folha de Sao Paulo reported last week.

(Editing by Cynthia Osterman)