Bond insurer Ambac Financial Group Inc. inched closer over the weekend to an agreement with a consortium of banks on plans to restructure the company and raise roughly $3 billion of capital, the Wall Street Journal reported today. MBIA, the biggest bond insurer, which has guaranteed $679 billion of debt, recently raised about $2.6 billion in capital to buttress its top-notch rating. Moody’s, S&P and Fitch Ratings have placed MBIA’s triple-A rating on watch for possible downgrade; a move to negative outlook would be considered by debt investors as an improvement in MBIA’s health. For Ambac policyholders, the most contentious issue has been a potential restructuring, which could effectively split Ambac’s low-risk municipal-bond business from its riskier structured-finance business. Ambac, the second-biggest insurer of bonds, guarantees the principal and interest payments on more than $550 billion in debt.