JAKARTA (REUTERS) - Indonesia's front-runner for July's presidential election received a significant boost to his chances of becoming leader of the world's third-biggest democracy on Tuesday after securing support from the country's number two political party.

Jakarta governor Joko "Jokowi" Widodo is already well ahead in opinion polls to win on July 9 and has the backing of two other parties.

"This is a step toward a coalition," business tycoon and head of the Golkar party Aburizal Bakrie told reporters at a local market in the capital where the two leaders met.

"Later, of course, if we can form a coalition, we will support Mr Jokowi to become president," he said.

Golkar came second in the April parliamentary election.

Jokowi's Indonesian Democratic Party-Struggle (PDI-P) came first in April but failed to win enough seats to meet the threshold to nominate a president by itself, forcing it to form a coalition with other parties.

But with the addition of Golkar, the parties supporting Jokowi would represent 49.44 per cent of the national vote in April's parliamentary election.

"Golkar has already said that they will support PDI-P and Jokowi as president. Them (Bakrie and Jokowi) standing together in that market is a symbol that the coalition is happening,"senior Golkar official David Tampubolon told Reuters.

"We will make another announcement about the official coalition after our (party meeting) on 17 May."

The winner of July's presidential election needs a simple majority. Failure to do so would force a run-off in September with the new government taking office the following month.

Jokowi told reporters that the agreement did not mean any deal had been cut on his running mate.

Media speculation has been rife that he will choose former vice-president Jusuf Kalla, who remains a popular figure and currently heads the Indonesian Red Cross.

Kalla is a member of Golkar, a party which was created as the parliamentary rubber stamp of long-serving autocrat Suharto until his downfall in 1998. The party has since managed to repair its image and strengthen is grass roots support. It is also seen as strongly pro-business.

The announcement came shortly after Jokowi's main rival, ex-general Prabowo Subianto, told reporters that he had chosen chief economic minister Hatta Rajasa as his running mate. Rajasa is head of the moderate Islamic PAN party.