* Investors focus on possible tapering of Fed's bond buying * Dollar index up, Treasuries fall * U.S. stocks turn lower, S&P 500 comes off high * Crude oil tumbles after jump in supplies By Ryan Vlastelica NEW YORK, May 22 (Reuters) - Stocks, bonds and currencies took a wild ride on Wednesday, as remarks by Federal Reserve Chairman Ben Bernanke failed to provide the clear picture investors had hoped for of the likely continuation of the U.S. central bank's bond-buying program, with sentiment ultimately driven by expectations of tapering. Remarks by Bernanke, in testimony to Congress, that the bond purchases would remain in place for now initially drove sharp gains on Wall Street and sent the dollar lower. But stocks slid and the dollar rose to a 4-1/2-year high against the yen after Bernanke said that if economic improvement continued, "We could in the next few meetings take a step down in our pace of purchases." Wall Street stocks posted their biggest daily decline since May 1, after earlier rising more than 1 percent and sending the Dow and S&P to record highs. Losses accelerated after minutes from the Fed's latest meeting showed that some officials were open to tapering large-scale asset purchases as early as the next policy meeting, to be held June 18-19. "The market was disappointed with the fact that they did not get complete clarity and a green light that the current QE measures are going to be in place quarter after quarter," said Wilmer Stith, portfolio manager at Wilmington Trust Investment Advisors in Wilmington, Delaware, who helps oversee $25 billion in assets. "The market was really hoping to get from Bernanke today certainty that tapering of quantitative easing is really not going to be in the picture in 2013." Based on Bernanke's comments, continued stimulus would be "data-dependent," said Stith, noting, that "just leaves the market in this sort of unsettled environment." The dollar rose near a 4-1/2-year high against the yen after Bernanke cited the risks of holding interest rates too low for too long, reversing early losses sparked by his comments that it was too soon to remove existing stimulus measures. The dollar peaked against the yen at 102.88 and hit a nine-month peak against the Swiss franc at 0.9774. U.S. Treasuries sold off on Bernanke's comments about possibly tapering bond purchases, with the yield on the 10-year note, which moves inversely to the price, crossing 2 percent. European shares ended 0.2 percent higher, with European markets closing before the release of the Fed minutes. The Fed's policy is widely credited with contributing to the S&P 500's rally of 16 percent so far in 2013, a surge that has taken the benchmark index to one new high after another, including on Wednesday before equities turned negative. The Dow Jones industrial average was down 80.41 points, or 0.52 percent, at 15,307.17. The Standard & Poor's 500 Index was down 13.81 points, or 0.83 percent, at 1,655.35. The Nasdaq Composite Index was down 38.82 points, or 1.11 percent, at 3,463.30. The benchmark 10-year U.S. Treasury note was down 30/32, with the yield at 2.035 percent, erasing early gains after Bernanke raised the possibility of reducing the Fed's bond purchases this year if economic growth improves further. The dollar index was up 0.5 percent against a basket of major currencies, near a three-year high of 84.37 struck last week. The euro fell 0.3 percent in a volatile session. The dollar index is up nearly 5 percent this year as investors favor the greenback on signs of growing economic momentum and talk of an early end to the Fed's stimulus effort. "The takeaway from (Bernanke's) speech is clear, which is that the Fed is serious about winding down QE and all of the speculation surrounding this possibility is validated," said Kathy Lien, managing director of FX Strategy for BK Asset Management in New York. JAPAN RISES Japan's Nikkei climbed 1.6 percent to a 5-1/2-year high after the Bank of Japan, as widely expected, maintained an aggressively loose policy that will inject up to $1.4 trillion into the financial system. The news kept the yen weaker against the dollar, which gained 0.4 percent to 102.86 yen. MSCI's broadest index of Asia-Pacific shares outside Japan eased 0.4 percent. COMMODITIES MIXED The debate over the Fed's next moves, and particularly the potential impact on the dollar and on growth, also dominated commodity markets. Gold fell 0.8 percent while copper rose 1.4 percent to its highest level in two weeks. Brent oil dropped 1.5 percent on data showing a surprise jump in U.S. gasoline stocks, suggesting that summer U.S. demand might not meet supply. U.S. crude futures fell 2.1 percent, with the decline accelerating after the Fed minutes.