LOS ANGELES - Accusing giant bond-rating firm Moody's Investors Service of withholding evidence documenting its role in the housing and Wall Street meltdown, Attorney General Edmund G. Brown Jr. today announced court action to force Moody's to explain why it gave its highest ratings to "risky and toxic" mortgage-backed securities that ultimately cost investors and taxpayers billions of dollars. Brown's action comes seven months after the Attorney General subpoenaed Moody's, but the firm has refused to comply with the subpoena. "The need for court action to enforce a state subpoena is highly unusual," Brown said, "because companies almost always comply without such a drastic step being necessary." But he said Moody's, which played a central role in the run-up to the collapse of housing prices, has refused to explain its ratings practices to the state. Moody's said responding to the state subpoena would be a "waste of time....