NEW YORK, March 31 (Reuters) - U.S. Treasury yields dipped on Wednesday morning on demand from traders rebalancing their portfolios for quarter-end, and ahead of President Joe Biden’s infrastructure spending announcement. Traders must rebalance their portfolios at the end of the month and quarter to account for the drop in maturity of a bond portfolio as time passes. In order to rebalance, traders buy longer-dated debt, which typically drives yields lower. Demand was evident at the long end of the curve with the 10-year yield last down 1.4 basis points at 1.710% after rising to a 14-month high on Tuesday. The 30-year bond yield was down 2.5 basis points at 2.370%. The move lower in yields on longer-dated debt flattened the yield curve. The flattening began late on Tuesday after the spread between two- and 10-year yields - the most commonly used measure of the yield curve - had earlier reached its widest since July 2015. The two- and 10-yield curve on Wednesday was down less than a basis point on the day, while the spread between the five- and 30-year yields was down 1.5 basis points on the day. There is “a little bit of a bid in the long end as we look towards extensions and rebalancing. Overall it has been a fairly quiet day. Even this stronger data has had a minimal impact,” said Justin Lederer, Treasury analyst and trader at Cantor Fitzgerald. “There are a lot of people looking over to finish the quarter,” said Lederer. Yields were little moved by reports earlier that U.S. private employers hired the most workers in six months in March as more Americans got vaccinated against COVID-19, pushing the economy toward a broader reopening. The dip in yields comes ahead of Biden’s infrastructure announcement later Wednesday in Pittsburgh. The plan could have a price tag as high as $4 trillion to pay for traditional roads and bridges while also addressing climate change and income equality. Such a plan would require an increase in debt issuance that would drive Treasury prices lower and yields higher. Wednesday’s dip in yields may therefore be a temporary move ahead of the announcement. “The Biden thing is definitely important. I do believe that we could continue to see higher rates,” said Lederer. “If the economy continues to show that it is gaining momentum, and inflation picks up, with all this money in the system, I think that higher rates is where we should be going.” (Reporting by Kate Duguid; editing by Jonathan Oatis)