By Andrea Shalal WASHINGTON (Reuters) -A top adviser to U.S. Treasury Secretary Janet Yellen warned on Tuesday that China’s foot-dragging on debt relief could burden dozens of low- and middle-income countries with years of debt servicing problems, lower growth and underinvestment. Yellen’s counselor Brent Neiman criticized China’s “unconventional” debt practices and its failure to move forward with debt relief at an event at the Peterson Institute for International Economics. “China’s enormous scale as a lender means its participation is essential,” Neiman said in the speech, first reported by…