Also last week, new questions arose in Washington about mortgage bond investors' willingness to continue funding the subprime sector to the extent that it has in recent years. At a conference organized by the Hudson Institute, two mortgage securities market experts-Joseph R. Mason, an economics professor at Drexel University, and Joshua Rosner, managing director of hedge fund adviser Graham Fisher & Co.-said the relaxation of lending standards during the housing boom years has led to a rising tide of subprime borrower delinquencies, and could send investors scurrying to the exit door, especially if home values also decline.