The U.S. government will prevail in its lawsuit accusing McGraw-Hill Cos. and its Standard & Poor’s unit of fraud, former Securities and Exchange Commission Chairman Arthur Levitt said.

The Justice Department this week sued McGraw-Hill, claiming that S&P deliberately understated the risk of bonds backed by mortgages made to the riskiest borrowers to win business from Wall Street banks. S&P rated more than $2.8 trillion of residential mortgage-backed securities and about $1.2 trillion of collateralized-debt obligations from September 2004 through October 2007, according to the complaint.