Moody's warns on GMAC mortgage bond servicing

NEW YORK, March 4 (Reuters) - Moody's Investors Service on Thursday said it may downgrade portions of 125 residential mortgage bonds based on unusual "cash management arrangements" of GMAC Mortgage LLC, which services loans in the securities.

The rating company said GMAC commingled cash flows from multiple bonds in a single custodial account, Moody's said in a statement. This allowed GMAC to use cash from loans in one bond for principal and interest payments on another, it said.

By allowing the commingling, it "increases the likelihood that some RMBS deals may not be able to recover the amounts 'borrowed' by the servicer to fund advances or another RMBS deal if a servicer bankruptcy were to occur," Moody's said.

This could give rise to competing claims in a bankruptcy proceeding, the rater said.

Downgrades based on mortgage servicing, rather than credit, may add to concerns of bond investors who have been long accustomed to harsh rating cuts as delinquencies and foreclosures increase losses.

GMAC Mortgage is a unit of Residential Capital LLC. Residential Capital is owned by GMAC Inc.

(Reporting by Al Yoon; Editing by Padraic Cassidy)