* 10-year yields fall to lowest since July 3 * Bernanke says plans to pare bond purchases is flexible * Traders see timing of tapering pushed back By Karen Brettell NEW YORK, July 17 (Reuters) - Treasuries yields fell to their lowest levels in two weeks on Wednesday after Federal Reserve Chairman Ben Bernanke said plans to pare its bond purchase program are not set in stone, pushing back expectations of when a pullback may begin. While sticking closely to a time line he first outlined last month that the Fed would halt bond buying by mid-2014, when unemployment was projected to be around 7 percent, Bernanke went out of his way to stress that nothing was certain. "Our asset purchases depend on economic and financial developments, but they are by no means on a preset course," he told the U.S. House of Representatives Financial Services Committee in prepared remarks. "It looks like the timeframe for tapering has been pushed out," said Sean Murphy, a Treasuries trader at Societe Generale in New York. "Guys were looking at September for the start of this tapering and he's pretty much made it clear that may not be the case." Benchmark 10-year Treasuries were last up 9/32 in price to yield 2.50 percent, the lowest level since July 3 and down from 2.55 percent before the comments. Bernanke will take questions from lawmakers after he presents the testimony at 10 a.m. EDT (1400 GMT).