ROCHESTER, N.Y. (Reuters) - The U.S. Federal Reserve should consider curtailing its $600 billion bond buying program if the economy grows faster than expected, a Fed official known for his criticism of the asset purchases said Thursday.

Charles Plosser, president of the Federal Reserve Bank of Philadelphia, said if bond buying doesn't deliver the hoped-for economic benefits, he would "not infer that we merely need to increase the size of the program."

Instead, that would be a signal for the Fed to rethink its analysis of the program's costs and benefits.

"If the economy grows more quickly than I currently anticipate, the purchase program will need to be reconsidered and perhaps curtailed before the full $600 billion in purchases is completed," he said in remarks prepared for delivery to an economic seminar in Rochester, New York.

Plosser said he remained somewhat skeptical that the controversial asset-buying plan, announced in November, would provide much of an economic lift.

The Fed hopes the purchases will spur a stronger recovery by driving down longer-term interest rates. But Plosser said the U.S. Treasury could achieve the same effect -- without the Fed's involvement -- by issuing more short-term securities and fewer long-term bonds.

The program has drawn complaints at home and abroad. Critics worry it will spawn asset bubbles and inflation overseas while doing little to help the U.S. economy.

Plosser, who will be a voting member of the Fed's monetary policy committee next year, said the risk of sustained deflation was remote, but if it happened the Fed ought to consider expanding the asset purchases. However, it would need to clearly explain that the intent was to combat deflation, not speed up the recovery.

The Philadelphia Fed president has a reputation as an inflation "hawk" and regularly expresses concern that the central bank's swollen balance sheet could provide the kindling for a dangerous spike in price pressures.

He reiterated Thursday that the latest round of asset purchases -- often referred to as "QE2" -- will complicate the Fed's eventual return to a normal monetary policy stance.

"Because the Fed's monetary policy must be forward looking, the hue and cry from many quarters may be quite loud when it is time to act," he said. "Even with the best of intentions, if we don't act aggressively and promptly, we may find ourselves behind the curve and at risk for substantial inflation."

Plosser expected unemployment to decline gradually, falling to around 8 percent or 8.5 percent by the end of next year. He said the latest asset purchase program would probably not do much to speed the healing process in the labor market.

"Thus, I think that the benefits of the purchase program may be modest," he said. (Reporting by Emily Flitter in Rochester; Writing by Emily Kaiser; Editing by Andrew Hay)