BRASILIA, Brazil (Reuters) -- Brazilian President Luiz Inacio Lula da Silva will choose either Vice- President Jose Alencar or veteran politician Ciro Gomes of the Brazilian Socialist Party as his running mate for October's election, the head of Lula's party said on Tuesday.

Ricardo Berzoini, president of the ruling Workers' Party (PT), told Reuters the decision would be made by June 10, about two weeks before the party's national convention on June 23.

He said Lula and the PT had opted not to pick a running mate from the Brazilian Democratic Movement Party, the biggest in Congress, although they are still hoping to forge an alliance.

Lula is widely expected to run for reelection, but he has not yet confirmed his candidacy ahead of an end-June deadline.

Berzoini said the party was already acting as if Lula's candidacy had been confirmed "because that is how the people are treating him." Opinion polls show Lula would handily beat the main opposition candidate, former Sao Paulo state Gov. Geraldo Alckmin, in an election.

"Alencar and Ciro (Gomes) are two great names, known nationally, with acknowledged political experience and are loyal allies," Berzoini said.

"We will pick one taking into account the needs for alliances" and political support, he said.

Alencar of the Brazilian Republican Party has strong political support in Minas Gerais state, Brazil's second biggest.

Gomes, who has twice been a presidential candidate and until March was national integration minister, has strong backing in the Northeast, where Lula already leads by a wide margin.

Alencar's party has links to the evangelical Universal Church of the Kingdom of God, whose influence in Brazil has been growing over the past few years.

So far, the PT has only been able to forge a formal alliance with the Communist Party, and Gomes' socialists could be a welcome addition.

The PT has said it would back Alencar if he decided to run for Senate.