* China's 1st-quarter GDP below expectations * Spanish, Italian debt yields rise * March US growth rises modestly, near expectations By Chris Reese NEW YORK, April 13 (Reuters) - U.S. Treasury debt prices rose on Friday, pushing benchmark yields below 2 percent, as falling stocks and worries over global economic growth fueled appetite for lower-risk assets. Treasuries started the day higher as below-forecast Chinese output data dented risk appetite, and debt prices also benefited from a flight into more secure assets caused by nervousness over the persistent euro zone debt crisis. Data showed China's gross domestic product expanded by 8.1 percent in the first quarter, the weakest pace in nearly three years and below an 8.3 percent forecast. Worries over the European debt crisis also pushed Spanish and Italian debt yields higher, with the cost of insuring Spain's debt hitting an all-time high. "Treasuries have once again found their footing after China's gross domestic product weakened more than expected, while Spain's 10-year yields jump back above 5.9 percent this morning," said William O'Donnell, head of U.S. Treasury strategy at RBS Securities in Stamford, Connecticut. Benchmark 10-year Treasury notes were trading 18/32 higher in price to yield 1.993 percent, down from 2.06 percent late Thursday. Thirty-year bonds were 1-11/32 higher in price to yield 3.14 percent from 3.21 percent. "The worry for the market this week remains Spanish debt yields which have somehow starting moving on whether the risk trade is on, or mostly off, ... or the fact that China's GDP is not the 9 percent whisper number but only 8.1 percent last night," said Chris Rupkey, chief financial economist at Bank of Tokyo-Mitsubishi UFJ in New York. The U.S. Federal Reserve on Friday was buying $1.5 billion to $2 billion of Treasuries maturing February 2036 through February 2042 as part of its latest stimulus program, which has been nicknamed "Operation Twist". Data showing U.S. consumer prices rose modestly in March, largely in line with expectations, had little impact on the Treasuries buying. The bullish tone was supported however by the Thomson Reuters/University of Michigan's preliminary reading on consumer sentiment for April, which dipped to 75.7 from 76.2 in March. Economists had expected the index to hold at last month's level.