TREASURIES-Bonds plunge as debt supply worries outweigh data

* Supply concerns hit bond prices

* Worry U.S. may be in same boat after S&P cuts UK outlook

* Prices weak despite host of normally bond-bullish events (Adds analyst quote, updates prices)

By Chris Reese

NEW YORK, May 21 (Reuters) - U.S. Treasuries plunged on Thursday after the government said it would sell a massive amount of new debt next week, adding to worries whether global investors can digest all the pending supply.

Bond investors were also mulling the value of U.S. debt after Standard & Poor's cut its credit outlook on the United Kingdom to negative from stable, with some fears that huge deficits may leave the United States in the same situation.

"There is going to be a huge amount of supply to feed the deficit -- that is what is going on here," said David Dietze, chief investment strategist at Point View Financial Services in Summit, New Jersey. "People are asking, if the UK is having problems like this then maybe U.S. sovereign debt is also not as solid."

Benchmark 10-year Treasury notes US10YT=RR were trading 28/32 lower in price for a yield of 3.30 percent, marking the highest yield in nearly two weeks, from 3.20 percent late on Wednesday. The 30-year bond US30YT=RR was trading 1-29/32 lower for a yield of 4.27 percent from 4.16 percent.

The U.S. Treasury said it will sell $101 billion of new notes next week, matching the size of a record-large weekly note sale in April.