NEW YORK, Nov 9 (Reuters) - Longer-dated U.S. Treasuries extended gains on Monday after an auction of $40 billion of three-year Treasury debt was met with solid demand.

Benchmark 10-year notes US10YT=RR were trading 6/32 higher in price to yield 3.48 percent, down from 3.51 percent late on Friday, while 30-year bonds US30YT=RR were 7/32 higher to yield 4.39 percent from 4.40 percent. (Reporting by Chris Reese)