(Adds quotes, details on stocks and Fed, updates prices) * Stock decline increases demand for bonds * U.S. 10-year yields lowest since March 1 By Karen Brettell NEW YORK, March 21 (Reuters) - U.S. Treasury yields fell to three-week lows on Tuesday as stock markets tumbled, raising demand for low-risk U.S. government debt, with analysts citing frustration with the pace of the Trump administration's fiscal plans as a factor behind the move. Wall Street fell sharply on Tuesday with the S&P 500 and Dow Jones Industrial Average down around 1 percent. They are on track for their worst one-day percentage declines since before Trump's election victory in November. "Stocks are down, and bonds are reacting to that," said Lou Brien, a market strategist at DRW Trading in Chicago. Analysts attributed the selling to reduced confidence that U.S. President Donald Trump's pro-growth policies, including financial deregulation, would be implemented soon. Trump is facing opposition from lawmakers on his plan to dismantle Obamacare, with any new fiscal stimulus likely to be delayed as the administration prioritizes domestic issues including healthcare. Benchmark 10-year U.S. Treasuries gained 11/32 in price to yield 2.43 percent, the lowest yield since March 1 and down from 2.50 percent earlier on Tuesday. Expectations of a less aggressive Federal Reserve than some investors had expected added to bond gains on Tuesday. Yields have fallen since the U.S. central bank last Wednesday raised interest rates, as expected. Some investors had anticipated the Fed would also take a more hawkish tone on future rate hikes on expectations of stronger growth. "They concentrated so much fire power toward the rate decision that they created this atmosphere of urgency in the minds of traders," said Jim Vogel, an interest rate strategist at FTN Financial in Memphis Tennessee. However, "when they actually sat down they said 'we've got to raise rates,' but they didn't display any urgency on any other point," Vogel said. The Fed reiterated that future rate increases would be "gradual." At the current pace, rates would not return to a neutral level until the end of 2019. Speeches by Fed officials are in focus this week for any new indications about future interest rate policy. Fed Chair Janet Yellen is due to speak at a community development conference on Thursday. The Federal Reserve sees an opportunity to remove some of the monetary stimulus it has given the U.S. economy, Kansas City Federal Reserve President Esther George said on Tuesday. Cleveland Fed President Loretta Mester and Boston Fed President Eric Rosengren are scheduled to speak later on Tuesday. (Reporting by Karen Brettell; Editing by Richard Chang) )