UPDATE 1-FASB changes accounting rules for US bond insurers

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NEW YORK, May 23 (Reuters) - In a move that could hurt U.S. bond insurers, the U.S. accounting rulemaker on Friday said it is changing standards for when the insurers have to set aside money for expected losses.

Under the new rule by the Financial Accounting Standards Board, insurers that have guaranteed bonds must boost their claims liabilities, or funds set aside to cover expected losses, when the bonds' credit quality has deteriorated.

At least some bond insurers currently set aside reserves only when they believe they can estimate the losses, and the losses are likely to take place. The new rule would force those insurers to set aside money sooner.

The two biggest U.S. bond insurers, MBIA Inc (MBI.N: Quote, Profile, Research, Stock Buzz) and Ambac Financial Group (ABK.N: Quote, Profile, Research, Stock Buzz), were not immediately available for comment.

The Financial Accounting Standards Board said the new rules are effective for periods starting after Dec. 15, 2008, which for most major bond insurers is the first quarter of 2009.

The new rule, called FASB Statement No. 163, also changes standards for recognizing revenue for financial guarantors. (Reporting by Dan Wilchins and Emily Chasan; Editing by Leslie Adler)