WASHINGTON, Oct. 31 — The Federal Reserve gave investors what they wanted today, lowering short-term rates for the second time in two months.

But it quietly warned Wall Street not to expected to assume that more reductions are ahead.

The move, to reduce short-term rates by a quarter point to 4.5 percent, was aimed at preventing the meltdown in housing from crippling the rest of the economy. But the vote was not unanimous, reflecting disagreement among policymakers about the risks that confront the economy.

Investors were generally pleased, and stocks were up modestly after briefly giving up most of their gains for the day immediately after the announcement. But Treasury prices fell, reflecting some concerns that lower interest rates could stoke inflation. Oil prices surged nearly 4 percent and gold futures were up about 1 percent. The dollar modestly weakened against other major currencies.

In a statement accompanying its decision, the Fed acknowledged that the housing collapse is likely to slow the economy. But it said “some inflation risks remain” and that the risks of inflation were “roughly balanced” against the risk of slower growth.