A pension fund is suing Moody’s Corp., charging the company misrepresented or failed to disclose that it assigned “excessively high” ratings to bonds backed by risky subprime mortgages.

In the suit filed yesterday in U. S. District Court in Manhattan, the Teamsters Local 282 Pension Trust Fund says Moody’s compromised subprime home loans, including bonds packaged as collateralized debt obligations, by assigning them such ratings.

Even as a downturn in the housing market raised concerns among homeowners and stockholders nationwide, Moody’s maintained those high ratings instead of downgrading its bonds to reflect the true risk of owning debt backed by subprime mortgages, the complaint says.

Moody’s disclosed on July 11 that it was downgrading nearly 400 mortgage-backed securities issued in 2006 and reviewing an additional 32 bonds for downgrade, which would affect $5.2 billion of bonds, and had already downgraded 52 bonds issued in 2005, according to the complaint.

The pension fund purchased Moody’s stock between October and July.

Following Moody’s July announcement, its stock price fell below $45 a share in August after trading at more than $60 in July and at more than $70 in June, according to the suit.

The suit also names the company’s chief financial officer and executive vice president, Linda Huber, charging she had access to the adverse undisclosed information about the company’s operations and had a duty to share truthful information with stockholders.

“Investors rely on these ratings to assess the value and risk of these investments,” the complaint says. “While the nation’s housing market was booming, Moody’s reaped millions of dollars in fees for assigning ratings to subprime-mortgage-backed securities.”

The pension fund is seeking class action status for all purchasers of Moody’s stock between October and July, and requests an unspecified amount of compensatory damages that result from Moody’s alleged wrongdoing.

A spokeswoman for Moody’s, Frances Laserson, said the company has not yet had a chance to review the complaint and had no comment.

More than a dozen homebuyers, shareholders, and investment banks have filed suit directly against their mortgage lenders since July.

The Securities and Exchange Commission is examining the accounting and disclosure issues to see if the credit-rating agencies followed proper protocol in rating the mortgage-backed securities, the SEC chairman, Christopher Cox, told a Senate committee yesterday.