Oct. 10 (Bloomberg) -- Morgan Stanley, the U.S. securities firm whose shares dropped 26 percent yesterday, had its long-term credit ratings put on review for a possible downgrade at Moody's Investors Service.

About $200 billion of long-term debt is affected by the review of Morgan Stanley's A1 credit rating, Moody's said in a statement today. The ratings agency affirmed its Prime-1 grade for Morgan Stanley's short-term debt.

To contact the reporter on this story: Christine Harper in New York at charper@bloomberg.net.

Last Updated: October 9, 2008 22:01 EDT