The Fed should set its guidance based on the economic outcomes it seeks and focus on buying more mortgage-backed securities, Rosengren said in a CNBC interview.

Without new stimulus, the jobless rate would rise to 8.4 percent at the end of this year and economic growth wouldn’t exceed its 1.75 percent average in the first half of the year, he said.

Editor's Note: You Owe It to Yourself to Know What Obama and Bernanke Are Hiding From Americans

“What I would argue for actually is to have it open-ended, that we focus on economic outcomes,” Rosengren said. “It would be setting a quantity that you’re going to continue to buy until you get the economic outcomes that you want.”

Additional accommodation is necessary because unemployment remains at the same 8.3 percent level it was in January even after the central bank has purchased $2.3 trillion in bonds and held its main interest rate near zero since December 2008, Rosengren said. The Boston Fed chief doesn’t have a vote on the policy-setting Federal Open Market Committee this year.

A new easing program “needs to be substantial enough that it offsets some of the shocks that we’re getting from abroad and some of the concerns that people have with how weak the world economy has been,” Rosengren said.

“We’re in a global slowdown. That would argue for a quantitative easing program, and one of sufficient magnitude that it has an impact.”

Operation Twist

The FOMC said Aug. 1 it will continue swapping $667 billion of short-term debt with longer-term securities to lengthen the average maturity of its holdings, an action dubbed Operation Twist. Policy makers also said they will “closely monitor” economic data. The FOMC next meets on Sept. 12-13.

“We want a stronger economy, we want faster growth in the incomes and we want a labor market that has an unemployment rate that’s clearly declining,” Rosengren said. “If you’re treading water even if you’re a good swimmer at some point you need to get to land.”

Rosengren, 55, was formerly the head of banking supervision and regulation at the Boston Fed and became its president in 2007. Fed presidents rotate voting on monetary policy, with Rosengren next holding a seat in 2013.

Editor's Note: You Owe It to Yourself to Know What Obama and Bernanke Are Hiding From Americans