A controversial proposal that could make it more difficult, and more expensive, to originate the priciest subprime mortgages could be finalized as early as next month. "Late summer is when we expect to have something out on that," said a spokesperson at the Federal Reserve Board of a proposal that would amend the Home Ownership and Equity Protection Act, the federal statute that governs so-called "high-cost" mortgages. But, a semiannual regulatory agenda published recently by