U.S. Federal Reserve officials, out on a speaking spree on Thursday, suggested the economy would have to deteriorate for the central bank to consider additional monetary stimulus.

Policymakers did hint at the possibility of further action. Fed Board Governor Sarah Raskin said the U.S. central bank stands ready to do all it can to support the economic rebound, while William Dudley, president of the New York Fed, emphasized the recovery's fragility.

Some economic news has been encouraging and may be suggesting that the pace of the recovery is picking up, Raskin said, citing the drop in the unemployment rate over the past six months and the creation of about 1 million jobs. However, the national economic recovery clearly has a long way to go.

Late Wednesday the Fed's influential vice chair, Janet Yellen, said the central bank's policy of near-zero interest rates is appropriate given high unemployment and the headwinds facing the economy. She added the central bank has a variety of options were it to engage in further asset purchases, and that the Fed remains quite willing to take whatever actions are necessary to achieve its mandate.

However, that message was not unanimous. While Yellen defended the Fed's guidance that it would likely leave rates near zero until late 2014, Philadelphia Fed President Charles Plosser on Thursday said the central bank should move away from the approach of suggesting a specific calendar date for the start of rate hikes.

I'd like to get us to move away from that and substitute something that's a little more systematic and coherent about how it depends on the economy, Plosser told reporters after a speech to economists.

The Fed next meets on April 24-25, and it is not expected to take any fresh policy measures at that time, but rather use the meeting to discuss the latest economic developments and further refinements to its communications strategy.

Still, a Reuters poll conducted after last week's release of disappointing March employment figures found most Wall Street primary dealers think another round of bond-buying will eventually take place.

Financial markets have been keenly attuned to any signs that the Fed might expand its asset-buying program, which it has used to stimulate the economy along with the decision to keep the official interest rates near zero. The easy money that has flooded markets has been viewed as a key factor in supporting asset values.

The Fed's Operation Twist program, which is designed to lower long-term interest rates by lengthening the average maturity of the Fed's bond portfolio, is to end in June.

BERNANKE UP TO BAT

Investors will be keen to see what Fed Chairman Ben Bernanke has to say on Friday when he gives the latest in a string of recent public pronouncements that included four lectures to college students last month.

Raskin said the Fed's actions have helped with business investment spending and she noted the pick-up in car sales. The lower value of the U.S. dollar has also helped exports, but the pace of recovery is still slow.

The Federal Reserve remains fully committed to doing everything it can to promote maximum employment in the context of stable prices, Raskin said in a speech to Los Angeles business and community leaders.

Still, investors were left with the sense that things would need to get worse for the central bank to act.

We believe it would take a significant weakening in the data before the committee would initiate further asset purchases, said Michael Gapen, economist at Barclays in New York.

Yellen said she expects the economic recovery to continue and to strengthen somewhat over time.

U.S. economic growth has been erratic during this recovery, and the job market has been especially slow to get into gear.

Gross domestic product registered growth of 3 percent in the fourth quarter of 2011, but growth is expected to have slowed to the low 2 percent range in the first three months of this year.

The unemployment rate has fallen from around 9.1 percent last summer to 8.2 percent in March. But employment growth slowed sharply last month as well, raising fears that the labor market might sputter out yet again.

The economy has made up less than half the jobs lost during the Great Recession, without adjusting for population growth.

Still, Plosser and others at the Fed argue further monetary stimulus would offer little additional boost to employment while raising the risk of inflation and complicating an eventual exit from the low rates policy.

Maximum employment is largely determined by factors that are beyond the control of monetary policy, he said.

(Additional reporting by Stella Dawson, Walter Brandimarte and David Bailey; Editing by Chizu Nomiyama and Leslie Adler)

Federal reserve Ben Bernanke