Rousseff, 62, currently the Cabinet chief, is being pushed forward by the ruling Workers Party as Brazil's first woman president-in-waiting. However, opposition candidate and Sao Paulo state Gov. Jose Serra continues to hold a lead, though opinion polls suggest he has lost ground.
Amid continued popularity, Lula is barred by law from seeking a third term but is widely seen poised to remain as the power behind the throne if, as expected by the ruling party, Rousseff wins election in October.
This week's opinion polls showed that Serra's lead could be narrowing as the ruling Workers' Party campaign for the Oct. 3 gains momentum. In the meantime, the polls showed that support for Rousseff jumped to 25 percent from 17 percent.
The Workers' Party is expected to endorse Rousseff as its candidate at a convention this weekend. Analysts attributed Rousseff's gains to Brazil's buoyant economy and Lula's enormous popularity. The Workers' Party is hoping to transform Lula's prosperity into votes for Rousseff.
Adding to Rousseff's strength is an unspoken national consensus, encompassing the opposition, that Lula's economic policy is working well for Brazil and a move away from its key features will only reverse Brazil's economic gains.
Brazil bounced back from recession in 2009 and current indicators suggest its economy is likely to grow by more than 5 percent this year. Economists cite Lula's economic policy, including a free-floating currency and a budget surplus, as the reasons behind the cross-party approval of his economic program.
The ruling Workers' Party has exploited support for Lula to advance the argument that the policies will be better looked after by a Lula protege than by an opposition candidate.
The October election is set to be a huge operation. In addition to electing a president and vice president, 135 million Brazilians will elect 27 state governors; a new Chamber of Deputies, two-thirds of the Senate; and 1,059 representatives to state assemblies.
Once the candidacies of Serra and Rousseff are confirmed they will step down from their current posts in April in order to run for the presidency.
But it will not be before June that parties will have conventions to confirm their candidates.