TREASURIES-Bonds tumble after 10-year auction

NEW YORK, June 10 (Reuters) - U.S. Treasuries plummeted on Wednesday and extended their losses after an auction of benchmark 10-year notes, in which investors drove a hard bargain for a higher yield to get the issue to market.

Though it was a reopening of a previously issued security, it was the first test of the government's long-term borrowing ability since investors began to wonder last month whether the United States' prized AAA credit rating may be living on borrowed time.

The existing 10-year Treasury note US10YT=RR was down as much as a full point on the day after the auction. It was last trading down 27/32, yielding 3.97 percent. Before the auction it was down 19/32, yielding 3.94 percent.

(Reporting by Burton Frierson)