There will be a “waterfall” of credit-rating cuts in the $2.93 trillion municipal debt market as ratings companies scrutinize state and local off-balance sheet liabilities, said Meredith Whitney, the banking analyst. The downgrades will force investors such as insurance companies to sell the securities, presenting an opportunity for other bond buyers, Whitney said on a radio interview today on “Bloomberg Surveillance” with Tom Keene. The analyst fueled a sell-off of tax-exempt debt when she said on CBS Corp.’s “60 Minutes” in December that there could be 50 to 100 “sizable” municipal-bond defaults in 2011 amounting to “hundreds of billions of dollars.”