(Adds comment from FSA spokesman in sixth paragraph)

NEW YORK, May 14 (Reuters) - Moody's Investors Service on Wednesday said it will reassess the mortgage exposures of top rated bond insurer Financial Security Assurance in light of its worse-than-expected losses from some mortgage bonds.

If the review results in higher loss expectations from FSA's exposure to bad mortgages, the company's cash cushion could be depleted, which in turn may pressure its "AAA" ratings, Moody's said in a statement.

Moody's currently has a stable outlook on the insurer, indicating a rating change is not anticipated over the next 12-to-18 months.

FSA, part of French-Belgian financial services group Dexia (DEXI.BR: Quote, Profile, Research), on Wednesday reported a net loss of $421.6 million in the first quarter versus $85.2 million profit a year ago, after taking almost $318 million of after-tax charges on credit default swaps and $195.3 million after-tax loss expenses on mortgage exposure.

The company incurred significant losses during the first quarter, with $333 million of loss reserve charges on direct home equity lines of credit (HELOC) and closed-end second lien residential mortgage-backed securities, Moody's said.

"We believe that we have reserved appropriately for losses in the HELOC and Alt-A closed-end second-lien mortgage portfolio," said FSA spokesman Tom Vogel.

The loss brings the insurer's cumulative loss reserve charge for its mortgage-related exposures to approximately $420 million, which is in line with Moody's prior expected case loss estimate for these exposures of $434 million, Moody's said.

(Reporting by Karen Brettell; Editing by Diane Craft)