* QE3 gets muted response after weeks of anticipation
* Buy the rumor, hold on the fact as oil, copper a little higher
* Gold highest since February; oil faces from 4-1/2 month high
NEW YORK, Sept 13 (Reuters) - Major commodity markets, including oil and copper, gave an initial tepid response to the Federal Reserve's third effort to revive the U.S. economy, leaving gold the biggest beneficiary of a plan that has been slowly baked into markets for weeks.
Prices jumped immediately on Thursday after the Fed said it had agreed to buy $40 billion of mortgage debt per month and continue to purchase assets until the outlook for jobs improves substantially, meeting broad expectations for a third set of quantitative easing to get growth back on track.
But an hour after the news hit, gold had extended gains to more than 2 percent or $35, reaching its highest since February at $1,765 an ounce, while oil and copper prices were only a bit firmer, having first lurched higher and then lower. November Brent crude was up 47 cents at $115.80 a barrel.
As the dust settled and traders awaited Chairman Ben Bernanke's press conference at 2:15 p.m. EDT (1815 GMT), a consensus emerged that the Fed plan offered no reason for despair, but likewise little cause for hope of an abrupt economic turn-around that might boost demand for raw materials.
"The Fed has taken the middle road with a modest, defined contribution purchase program and extended rate guidance," said Joseph Trevisani, chief market strategist at Worldwide Markets in Woodcliff Lake, New Jersey.
In a plan that offered relatively few surprises, meeting expectations for more bond buying and an extension of the Fed's ultra-low interest rate pledge to mid-2015, the most significant shift was the committee's decision to tie the duration of its bond binge to economic conditions, rather than a finite sum.
U.S. stock markets pushed higher as the news settled in, rising 1 percent. The U.S. dollar index fell 0.35 percent.