SAO PAULO (Reuters) - Brazilian President Dilma Rousseff's popularity has plunged by nearly half since her recent re-election as a severe government corruption scandal, an economic slowdown and surging prices for electricity, gasoline and bus fares left voters feeling misled.

The Datafolha poll of 4,000 people published on Saturday showed those interviewed who rated Rousseff's performance as "excellent or good" fell to 23 percent from 42 percent in December, just after she won her second term in a tight race.

Over the same period the percentage of people who rated her as a "bad or terrible" president rose to 44 from 24 percent. It was the first time since Rousseff took office in 2011 that she received more negative marks than positive ones.

The remainder of respondents, 33 percent, rated Rousseff's government as average, which was unchanged since December.

Rousseff promised during last year's campaign that she would not have to dramatically raise utility prices or slash government spending, but since her October re-election she has done both to try to regain investor confidence and revive an economy that has sputtered since she took office.

The economy is expected to shrink in the first months of the year, annualized inflation is above 7 percent and rising, and many Brazilians are facing the possibility of water and energy shortages due to a prolonged drought.

Sixty percent of respondents said they believed Rousseff had lied more than she told the truth during the campaign.

Meanwhile, 77 percent of respondents said they believed Rousseff knew about corruption in the state-run oil company Petrobras, which she has controlled for several years as president and previously during the administration of Luiz Inacio Lula da Silva, when she was chairwoman of the board.

Rousseff has denied any knowledge of the graft scheme, which investigators say siphoned billions of dollars.

The worsening of Rousseff's image was consistent across age groups, but the poorest socioeconomic groups, who benefited most from the policies of Rousseff and her mentor Lula, showed less disapproval than higher income earners. The rich showed the highest disapproval.