Mitsui Trust & Banking Co. announced a sweeping corporate restructuring plan Friday that calls for it to retreat from overseas banking by the end of March and concentrate on domestic asset trust services in tandem with a U.S. firm.As part of the streamlining, executive bonuses will be cut 10 percent beginning this month and 600 jobs will be axed from the current payroll of 5,600 by March 31, 2000.In addition, Mitsui Trust Securities Co. will be disposed of, although no decision has been made on how to liquidate the subsidiary.Mitsui's hope is to enhance its domestic foothold and build on its capital base by pulling out of less profitable overseas banking operations. Toward that end, the withdrawal from overseas will give Mitsui Trust an opportunity to unload some of its nonperforming loans.Investors reacted favorably to the announcement; Mitsui Trust shares shot up 16 yen to 152 yen on the Tokyo Stock Exchange.Kiichiro Furusawa, vice president of Mitsui Trust, told a news conference Friday that the firm will close down its branch offices in New York, London and Hong Kong plus a subsidiary in Hong Kong by the end of March. "The pullout from global banking comes in line with our restructuring plan announced in January," he said. "We estimate we can reduce up to 7 billion yen in operational costs."The subsidiaries in New York and London will return their banking licenses and become investment-advisory firms. The bank's other overseas assets will be sold, Furusawa said.Ironically, by withdrawing from global banking, Mitsui Trust will be able to beef up its capital-adequacy ratio above and beyond the internationally accepted 8 percent. Furusawa said the bank is looking at an 11 percent ratio.But the withdrawal means the bank will only be bound by the 4 percent domestic standard set by the Japanese government.In a move to strengthen its asset management business in Japan, the bank said it has struck a broad-based tieup with State Street Bank and Trust Co. of the United States, under which the two firms will jointly provide custody services related to investment trusts.