* ECB expected to intervene to stem euro zone crisis * Benchmark yields bumping against support at 1.87 pct * Fed to buy shorter-dated Treasuries as part of Twist By Chris Reese NEW YORK, Aug 21 (Reuters) - U.S. Treasury debt prices eased on Tuesday as investors turned to riskier assets due to expectations the European Central Bank will eventually intervene to ease the euro zone debt crisis, although lack of detail about any plans limited losses. Investors cited a story in British newspaper The Daily Telegraph which said it could confirm an earlier report in German media that ECB experts were examining plans to effectively cap Spanish and Italian bond yields. The ECB tried to quash speculation on Monday that it would target specific interest rate thresholds as part of any bond-buying program. On Tuesday, it reiterated the statement. Uncertainty about the ECB plans is high. Investors are also concerned the ECB's condition that troubled countries need to ask for help from the euro zone's rescue funds before getting assistance from the central bank may mean that the Spanish crisis could get worse before it gets better. Still, some optimism over eventual ECB action had investors looking to take on riskier assets, and German Bund futures fell while Italian and Spanish debt yields dipped. Wall Street stocks were making a run at a four-year high. "The market has moved to the belief that (the ECB) is going to do whatever it takes," said William Larkin, fixed income portfolio manager at Cabot Money Management in Salem, Massachusetts. He added fears over the eventual outcome of Europe's debt crisis, along with worries over the pace of global growth, had pushed Treasury debt prices to levels that many investors considered to be overly expensive. Benchmark yields have generally been rising since hitting a record low of 1.38 percent in late July. Ten-year notes on Tuesday were trading 7/32 lower in price to yield 1.83 percent, up from 1.81 percent late Monday. Losses were also limited by technical factors, with the 200-day moving average at 1.87 percent capping this month's rising trend in 10-year yields on the back of some improvement in U.S. economic data. Investors are speculating on whether the Federal Reserve will step in with another round of economic stimulus, and will parse through the minutes of the central bank's last policy meeting, set for release on Wednesday, for any clues as to whether more quantitative easing is on the way. The Fed itself will sell shorter-dated Treasuries on Tuesday as part of its current stimulus program, which has been dubbed "Operation Twist." The Fed is selling shorter-dated U.S. government debt and buying longer-dated Treasuries in an effort to lower longer-term borrowing costs like those on mortgages.