(Updates with market activity, economist comment) By Ross Kerber April 20 (Reuters) - Investors sent most U.S. Treasury yields lower on Tuesday as they moved out of stocks and eyed challenges many countries still face from the COVID-19 pandemic. The benchmark 10-year yield was down 3.5 basis points at 1.5642% in early afternoon trading after spending much of the morning near 1.6%. The move down in yields came as the S&P 500 and the Dow traded lower for a second straight day, with investors pinning their hopes on results from Netflix and other major tech-related companies this week to help sustain an upbeat start to the earnings season. Tufts University economist Brian Bethune said the lower yields stood in contrast with their level close to 1.8% on March 30 and showed investors worried that public health gains against the virus have stalled in Brazil, Canada and other countries. Even though the U.S. economic recovery looks strong, Bethune said, "There"s a repricing of what the international environment is going to look like." The benchmark yield remained above its multi-week low of 1.528% reached April 15. Investors will watch the results of a $24 billion auction of 20-year bonds by the U.S. Treasury set for Wednesday. U.S. Federal Reserve Chair Jerome Powell said the U.S. economy will temporarily see "a little higher" inflation this year as activity strengthens and supply constraints push up prices in some sectors, but the Fed is committed to keeping any overshoot within limits, according to an April 8 letter seen by Reuters. A closely watched part of the U.S. Treasury yield curve measuring the gap between yields on two- and 10-year Treasury notes, seen as an indicator of economic expectations, was at 141 basis points, about 4 basis points lower than Monday"s close. The two-year U.S. Treasury yield, which typically moves in step with interest rate expectations, was down less than a basis point at 0.1532%. April 20 Tuesday 12:46 PM New York / 1646 GMT Price Current Net Yield % Change (bps) Three-month bills 0.0275 0.0279 0.000 Six-month bills 0.0425 0.0431 0.000 Two-year note 99-242/256 0.1532 -0.008 Three-year note 100-40/256 0.3223 -0.019 Five-year note 99-198/256 0.7968 -0.032 Seven-year note 100-24/256 1.2358 -0.036 10-year note 96-4/256 1.5642 -0.035 20-year bond 95-144/256 2.1511 -0.028 30-year bond 91-164/256 2.2619 -0.031 DOLLAR SWAP SPREADS Last (bps) Net Change (bps) U.S. 2-year dollar swap 11.50 0.25 spread U.S. 3-year dollar swap 12.25 0.50 spread U.S. 5-year dollar swap 8.50 0.75 spread U.S. 10-year dollar swap -1.50 0.75 spread U.S. 30-year dollar swap -28.25 1.00 spread (Reporting by Ross Kerber in Boston; Editing by Susan Fenton and Steve Orlofsky)