Slower prepayments by less credit-worthy borrowers could mean higher losses on adjustable-rate mortgage pools, a new report by Moody’s Investors Service suggests. And the outlook for newer vintages of fixed-rate loans may not be so rosy either. "In general, Moody’s expects losses on subprime ARM pools to be 20 percent to 30 percent higher than on fixed-rate mortgage pools from the same originator," the rating agency said in its June 22 analysis. But on loans