By Gavin Jones

ROME (Reuters) - Italy's wealthy northern regions of Lombardy and Veneto, controlled by the right-wing Northern League, will hold referendums in October to try to obtain greater autonomy from the central government, Lombardy's president said on Thursday.

The result of the ballots will not be binding but a victory could strengthen the League and raise the profile of the popular governor of Veneto, Luca Zaia, widely seen as a potential leader of Italy's center-right.

"The referendums will be in October," Lombardy President Roberto Maroni told reporters in Milan, saying the date would be announced later this week.

Italy's Constitutional Court threw out Zaia's original plan to ask voters if they wanted Veneto to secede from Italy or keep control of 80 percent of tax revenue collected in the region.

Instead the question on the ballot paper will be: "Do you want Veneto to be given further forms and particular conditions of autonomy?" The question for Lombardy has not yet been set.

Tax remains the key issue. Lombardy, around Milan, is Italy's commercial hub and accounts for roughly a fifth of the country's gross domestic product, while Veneto produces just under 10 percent of the national GDP.

Many inhabitants resent seeing a large part of their taxes used to help finance services in poorer southern regions.

The League hopes a big victory for "yes" on a high turnout will give it greater bargaining power in negotiations on fiscal policy with the government of Prime Minister Paolo Gentiloni.

It also hopes the campaign will boost its support ahead of a parliamentary election due in early 2018.

The party, which campaigns on an anti-euro, anti-immigrant platform, has the backing of 12 percent of voters, opinion polls show, making it Italy's third or fourth biggest party and the joint largest in the fragmented centre-right.

Its leader Matteo Salvini officially backs the referendums even though they may not help his efforts to expand the party's appeal outside its northern heartland. So far, his drive to turn the League into a more national party, with frequent visits to southern cities, appear to have had little success.

The main beneficiary of the regional votes may be Zaia, who has won plaudits as head of Veneto since 2010 and is seen as a potential threat to Salvini as leader of the League and of Italy's centre-right as a whole.

Zaia, a former agriculture minister, has a more moderate, pragmatic image than Salvini and is more popular among supporters of former prime minister Silvio Berlusconi's Forza Italia, the other main party in the centre-right bloc.

"The referendum is an ideal springboard for Zaia," said Francesco Galietti, head of political risk consultancy Policy Sonar. "He may go for Salvini's jugular if he can bring thousands of people to the polls and pull off a big success."

(Editing by Crispian Balmer and Janet Lawrence)