(New throughout) By Kate Duguid NEW YORK, Dec 11 (Reuters) - A risk-off move drove Treasury yields down across maturities on Friday, with the two-year yield falling to a four-month low, furthering speculation that the Federal Reserve may announce adjustments to its Treasury purchases at next week"s meeting. The fall in yields was partly attributable to reports that congressional wrangling over a spending package and coronavirus aid could drag on through Christmas. Also pulling yields lower was news that European pharmaceutical companies Sanofi SA and GlaxoSmithKline Plc would delay the launch of their COVID-19 vaccine until late next year, a setback in the global fight against the pandemic. Those macroeconomic drivers explain the fall in the benchmark 10-year yield and the 30-year bond yield to their lowest since Dec. 1. In afternoon trade, both had pulled back from those lows, with the 10-year last down 1.5 basis points at 0.892% and the 30-year down 1.4 basis points at 1.622%. The move in the two-year yield to its lowest since Aug. 7, however, was surprising, as the yield has been roughly anchored since the Fed moved interest rates to zero at the beginning of the pandemic. It was last down 2 basis points at 0.119%. Analysts argued the two-year move was likely not purely the result of macroeconomic drivers. Yields on Treasury bills - debt with a maturity of one year or less - are all less than 10 basis points away from 0%, according to Tradeweb data. "The idea that bills could potentially go to zero is taking twos, threes and fives along with it," said Justin Lederer, Treasury analyst and trader at Cantor Fitzgerald. Since the lows hit in March, the 10-year yield has risen more than 60 basis points, and the 30-year has risen nearly 100. The two-year yield, by comparison, was just a basis point and a half higher than the all-time low it hit in May. Both long rates have increased enough in the past several months that some analysts believe the Fed will purchase more longer-dated debt to cap yields and keep borrowing costs low. Since March the Fed has bought more than $2 trillion worth of Treasury debt, most of it in shorter-dated notes. If the Fed were to lengthen the average maturity of its Treasury holdings - by purchasing the same amount but buying more longer-dated debt and less shorter-dated debt - it could also have the effect of bolstering Treasury bills and shorter-dated notes away from zero. "I can see the Fed trying to do something to alleviate that. They definitely don"t want bills trading negative, or repo trading negative," said Lederer. December 11 Friday 4:14PM New York / 2114 GMT Price Current Net Yield % Change (bps) Three-month bills 0.0725 0.0735 -0.006 Six-month bills 0.0825 0.0837 0.000 Two-year note 100-3/256 0.119 -0.020 Three-year note 99-216/256 0.1772 -0.019 Five-year note 100-16/256 0.3623 -0.021 Seven-year note 100 0.625 -0.021 10-year note 99-212/256 0.8931 -0.015 20-year bond 99-76/256 1.4156 -0.016 30-year bond 100-12/256 1.623 -0.013 DOLLAR SWAP SPREADS Last (bps) Net Change (bps) U.S. 2-year dollar swap 7.50 0.25 spread U.S. 3-year dollar swap 6.00 0.00 spread U.S. 5-year dollar swap 5.50 0.00 spread U.S. 10-year dollar swap -1.00 -0.50 spread U.S. 30-year dollar swap -29.00 -1.00 spread (Reporting by Kate Duguid; Editing by Ken Ferris and Jonathan Oatis)