* Yellen wants easier policy than Wall Street expects * Fed No. 2 voices strong support for policy "thresholds" * Yellen: worth above-target inflation to cut unemployment By Braden Reddall BERKELEY, Calif., Nov 13 (Reuters) - Federal Reserve Vice Chair Janet Yellen said on Tuesday that U.S. short term interest rates may need to stay near zero until early 2016, a half year longer than Wall Street dealers expect, to forcefully lift employment. The central bank's No. 2 official, viewed as a front-runner to succeed Fed Chairman Ben Bernanke when his term expires in January 2014, also said she strongly backed adopting inflation and unemployment thresholds to guide policy. That would allow the Fed to move away from shaping financial market expectations with calendar dates. After its last meeting in October, the Fed reiterated that it expected to keep the overnight federal funds rate near zero until at least mid-2015. Yellen, however, argued an optimal policy would keep rates on hold for longer at the cost of a bit more inflation. "This highly accommodative policy path generates a faster reduction in unemployment than in the baseline, while inflation overshoots the (Fed policy) committee's 2.0 percent objective for several years," she told students at the Haas School of Business at the University of California, Berkeley. As a baseline, Yellen used an early September consensus from Wall Street firms, which showed they expected rates to remain near zero only through the first half of 2015. Yellen is regarded as one of the more dovish members of the Fed's policy-setting committee in her willingness to support aggressive efforts to spur job growth, but her analytical skills give her arguments weight in the policy debate. The Fed cut overnight rates to near zero in December 2008 and it has bought around $2.3 trillion in securities to drive other borrowing costs down and spur a stronger recovery. While there are signs the economy is gaining a bit of speed, the jobless rate remains stubbornly high at 7.9 percent. POLICY PATIENCE In January, the Fed adopted what it termed a "balanced approach" to its mandated goals of full employment and stable prices, suggesting it would temporarily tolerate a bit more inflation to move the jobless rate lower. On prices, it normally targets 2.0 percent inflation and policymakers' current estimates suggest they view an unemployment rate of between 5.2 percent and 6.0 percent as consistent with maximum employment. Yellen made clear that she does not view the inflation target as a ceiling and that slightly higher inflation may well be needed for the Fed to fulfill its promise to pursue a "balanced" monetary policy. "The optimal policy to implement this 'balanced approach' to minimize deviations from the inflation and unemployment goals involves keeping the federal funds rate close to zero until early 2016," she said. She said rates would stay below the path expected by Wall Street dealers through 2018. COMMUNICATING ON COMMUNICATIONS Yellen stressed that communicating Fed intentions clearly was vital to the success of its policies, and emphatically endorsed adopting numerical thresholds for unemployment and inflation to guide expectations on when rates would go back up. "Several of my ... colleagues have advocated such an approach and I am also strongly supportive," she said. Chicago Federal Reserve Bank President Charles Evans has suggested holding rates steady until unemployment is under 7.0 percent, provided inflation remains below 3.0 percent. Minneapolis Fed chief Narayana Kocherlakota outlined thresholds of 5.5 percent unemployment and 2.25 percent inflation. "The idea is to define a zone of combinations of the unemployment rate and inflation within which the (Fed) would continue to hold the federal funds rate in its current, near-zero range," Yellen said. She said that would help shape expectations of the Fed's likely response to incoming data. Even so, she said the thresholds would not trigger a rate hike decision. That, she said, would require "further committee deliberation and judgment." The central bank is also considering issuing a forecast that would represent the consensus of its 19 individual policymakers to give a better sense of the views driving Fed decisions. Currently, it provides a range of individual forecasts. Yellen, who is leading the Fed's efforts on communications, said it was proving "exceptionally difficult" to forge a consensus on the outlook for the economy.