St. Louis Federal Reserve President James Bullard said on Thursday that while the central bank's massive bond buying program impacted financial markets immediately, its effect on the broad economy will lag by as much as a year.

The effects of QE2 (the second round of quantitative easing) would be expected to lag by six to 12 months, Bullard said at a conference.

Gauging the effects of the easing program on the economy is complicated by shocks experienced in early 2011, he said. Fed policymakers have blamed disruptions from the devastating earthquake in Japan and the European debt crisis for slowing the economic recovery.

The Fed's $600 billion Treasury security buying initiative, aimed at providing a boost to the flagging economic recovery, had the same effect on financial markets as a substantial interest rate cut, Bullard said.

The Fed's bond buying program ends on Thursday, and the Fed has signaled it is not immediately planning to renew it. Fed Chairman Ben Bernanke said last week that while the recovery is still weak, rising inflation means economic conditions are different than those that led the Fed to launch the initiative in November.

Many academics, including some presenting papers at a conference sponsored by the St. Louis Fed at which Bullard spoke, say quantitative easing has been an effective monetary policy tool when interest rates are near zero.

However, many others have harshly criticized the program for risking inflation and contributing to rises in food and energy costs around the world. Others have questioned its effectiveness.

The Fed cut benchmark interest rates to near zero in December 2008 as the economy slowed during a wrenching financial panic and has kept them there since then.

(Reporting by Mark Felsenthal; Editing by Andrea Ricci)