U.S. government debt prices rose on Tuesday, as persistent worries about the economy and pending index changes rekindled bond purchases and pushed down longer-dated yields from one-month highs. Adding to the rebound in bonds for a second day was chatter whether the Federal Reserve would increase its balance sheet to buy more Treasuries on top of what it has been purchasing with funds that come from maturing mortgage securities. Traders, with their renewed enthusiasm for bonds, brushed aside gains on Wall Street and government data that showed sturdy consumer spending in August.