WASHINGTON — Foreign demand for U.S. Treasury securities rose to a record high in March. China, the largest buyer of Treasury debt, increased its holdings for a third straight month. Total foreign holdings rose 0.3 percent to a $5.12 trillion, marking the eighth consecutive monthly increase, the Treasury Department reported Tuesday. U.S. government debt is considered one of the safest investments. Demand has increased as investors worry about the uncertainty surrounding Europe’s debt crisis. China boosted its holdings 1.3 percent to $1.17 trillion, its third straight increase. China had trimmed its holdings for five straight months before the January increase....