Alan Greenspan, in one of his last appearances before Congress as Federal Reserve chairman, told lawmakers on Wednesday the U.S. growth outlook was solid and the Fed will keep lifting interest rates. But he warned "significant uncertainties" confront this positive prospect, including high energy prices, labor costs, the future path of long-term interest rates and the danger this could spell for the country's housing market, Reuters reported. "Our baseline outlook for the U.S. economy is one of sustained economic growth and contained inflation pressures," he told the House of Representatives Financial Services Committee in the first of two days of semiannual testimony on the economy and monetary policy. "In our view, realizing this outcome will require the Federal Reserve to continue to remove monetary accommodation. This generally favorable outlook, however, is attended by some significant uncertainties that warrant careful scrutiny." Stock prices initially softened but then pushed ahead, with the S&P 500 index, one of the broadest measures of U.S. equities, pushing to a new 4-year high. --SP 2304 Local Time 2004 GMT