WASHINGTON — The Federal Reserve lowered interest rates by a quarter of a percentage point on Wednesday, its second cut since late July, and suggested it was prepared to move aggressively if the United States economy showed additional signs of weakening.

For now, a growing number of Fed officials expect one more cut this year, based on economic projections released after the Fed’s two-day meeting. But a murky economic outlook and a division within the Fed’s policy-setting committee prevented a clear message about what comes next.

Jerome H. Powell, the Fed chair, said at a news conference after the meeting that the United States economy remained strong and unemployment low, but that “there are risks to this positive outlook.” If the economy weakens, he said, a “more extensive sequence” of rate cuts could be appropriate.

“Our eyes are open, we’re watching the situation,” Mr. Powell said, explaining that the Fed would stop cutting rates to sustain the expansion only “when we think we’ve done enough.”