American International Group Inc., the insurer bailed out by the U.S., said Chairman Steve Miller would be interim chief executive officer if CEO Robert Benmosche is unable to do the job while fighting cancer.

Miller will take the post “in the event that Bob would become unwilling or unable to continue to effectively serve in his current role,” the board of the New York-based insurer said today in a statement. Miller, 68, would have the job “for as long as it takes to identify and select a long-term replacement.”

Benmosche, 66, told staff on Oct. 25 that he had begun an “aggressive round of chemotherapy” and that the company was preparing for alternatives if he had to limit his work. AIG is focusing on global property-casualty coverage and U.S. life insurance and retirement services after striking deals to sell non-U.S. life insurers and consumer-finance operations to help repay the U.S.

Benmosche “continues to perform his job very well, and we have no reason to expect otherwise going forward,” said the board. The directors will continue their search for a permanent replacement on the expectation Benmosche will step down in 2012 as he indicated he would before telling staff of his diagnosis.

Benmosche joined AIG in August 2009, becoming the insurer’s fourth CEO since June of 2008. He was CEO of MetLife Inc. for eight years, transforming that company into the largest publicly traded U.S. life insurer from a mutual owned by customers.

AIG’s managers are seeking to attract private investors as the U.S. winds down its stake in the company. The insurer said in August that it may sell bonds for the first time since it was rescued in 2008.

The insurer announced plans in September to repay its debt on a Federal Reserve credit line and convert the Treasury Department’s $49 billion preferred stake into common stock for sale to private investors.