A leading bond and mortgage insurer, MBIA (ticker: MBI), Wednesday unveiled a comprehensive plan aimed at strengthening its capital in order to maintain its crucial AAA rating amid the mortgage-market massacre. MBIA was the first in its industry to take such action. Part of the company's effort calls for a 62% reduction in its quarterly common dividend, to 13 cents a share from 34 cents, to preserve some $80 million annually. MBIA had boosted dividends every year since initiating them in 1987. The Armonk, N.Y., company also intends to sell about $1 billion in notes due in 2033. In December, Warburg Pincus LLC agreed to commit up to $1 billion to help boost MBIA's capital. Nonetheless, MBIA's shares, which trade on the Big Board, sank to a 16-year low of 11.11 Wednesday. Friday, they were changing hands around 17. The proposed dividend cut would give the stock a current yield of 3.13%, versus 8.19%.