* U.S. 10-year, 20-year, 30-year yields fall to 3-week lows * U.S. two-year note auction shows decent results * Investors focus on FOMC meeting next week * U.S. coronavirus deaths surge to nearly 420,000 (Adds new comment, results of U.S. two-year note auction; updates prices) By Gertrude Chavez-Dreyfuss NEW YORK, Jan 25 (Reuters) - U.S. Treasury prices rose, pushing long-dated yields to three-week lows on Monday, as risk appetite ebbed amid persistent worries about surging virus cases and their potential for prolonged lockdowns that could further weigh on economic growth. Drugmaker Merck ending its COVID-19 vaccine program as well as doubts resurfacing about whether the Biden administration"s proposed $1.9 trillion stimulus plan could push through in Congress, also weighed on U.S. yields. Yields on benchmark 10-year, 20-year, and 30-year securities fell to three-week troughs. The yield curve also flattened on Monday, in line with the fall in long bond yields, with the gap between U.S. two-year and 10-year notes dropping to 91.50 basis points, its narrowest spread in three weeks. "There have been more concerns about the resurgence in the virus: the mutant strains, and the more strict lockdowns are weighing more on growth than was hoped for previously," said Kim Rupert, managing director of global fixed income analysis at Action Economics in San Francisco. U.S. coronavirus deaths surged to nearly 420,000 late on Sunday, with 25 million known cases, according to a Reuters tally. Tom di Galoma, managing director at Seaport Global in New York, also said the rally in Treasuries extended after Merck pulled out of its COVID vaccine plan. Merck & Co said on Monday it would stop development of its two COVID-19 vaccines and focus pandemic research on treatments, with initial data on an experimental oral antiviral expected by the end of March. In early afternoon trading, the U.S. benchmark 10-year yield fell to 1.044%, from 1.091% late on Friday. It earlier fell to 1.038%, its lowest since Jan. 7. U.S. 30-year yields slid to 1.8% from Friday"s 1.856%, after earlier dropping to a three-week low of 1.791%. U.S. 20-year bond yields also weakened to a three-week trough and were last down at 1.608%. "Technicals have capped the upside in rates," Action"s Rupert said. "Rates have been under pressure for a while, so we saw long-term rates pop up to their highest level in nearly a year. So we"re still kind of retreating from those levels." On the front end of the curve, U.S. two-year yields were down slightly at 0.12%, from 0.125% on Friday. The break-even inflation rate on 10-year TIPS, meanwhile, which measures expected annual inflation for the next 10 years, dropped to its lowest since late December. It was last at 2.015%, down from Friday"s 2.017%. Also on Monday, the Treasury"s $60 billion auction of U.S. two-year notes showed decent results. The high yield of 0.125% was below the "when-issued" level or consensus estimate at the bid deadline. The bid-to-cover ratio, a gauge of demand, was solid at 2.67 versus an average of 2.52. Indirect bidders, which include foreign central banks, took 56.6% of supply, compared with an average of 50.6%. Investors are also on focused on this week"s Federal Open Market Committee meeting. "Given the consistent refrain from policymakers of rates at the effective lower bound and QE (quantitative easing) continuing at the current pace, there is limited scope for any hawkish surprise," BMO wrote in Monday"s note. January 25 Monday 1:28PM New York / 1828 GMT Price Current Net Yield % Change (bps) Three-month bills 0.075 0.0761 -0.003 Six-month bills 0.085 0.0862 -0.003 Two-year note 100-2/256 0.1209 -0.004 Three-year note 99-216/256 0.1778 -0.010 Five-year note 99-210/256 0.4119 -0.022 Seven-year note 99-72/256 0.7316 -0.032 10-year note 98-100/256 1.0482 -0.043 20-year bond 95-248/256 1.6136 -0.045 30-year bond 95-212/256 1.8066 -0.049 DOLLAR SWAP SPREADS Last (bps) Net Change (bps) U.S. 2-year dollar swap 7.50 0.00 spread U.S. 3-year dollar swap 8.00 0.25 spread U.S. 5-year dollar swap 9.75 0.50 spread U.S. 10-year dollar swap 2.75 0.75 spread U.S. 30-year dollar swap -24.00 0.75 spread (Reporting by Gertrude Chavez-Dreyfuss; Editing by Will Dunham and Andrea Ricci)