Exclusive: Ally assumes it will lose entire GM leasing business - CEO

NEW YORK (Reuters) - Ally Financial Inc's new chief executive said on Thursday that he expects General Motors Co to eventually end all of its leasing agreements with the bank, threatening to cut off around a quarter of its retail lending business.

In January, the automaker said its in-house financing arm GM Financial would replace Ally as the exclusive lessor for Buick, GMC and Cadillac vehicles. Ally expects GM Financial to eventually take over leasing for Chevrolet and the rest of GM's brands, Chief Executive Jeffrey Brown said in an interview.

"Through time that is a planning assumption we've got today," Brown told Reuters.

A GM spokesman told Reuters that even though the automaker is boosting the capability and scale of GM Financial, it expects Ally to continue to play a role supporting GM dealers and customers.

(Reporting by Peter Rudegeair; Editing by Christian Plumb)