The Fed is likely to announce at the end of a two-day meeting that it will no longer add to its holdings of Treasury bonds and mortgage-backed securities, halting the final $15 billion in monthly purchases under a program that at its peak pumped $85 billion a month into the financial system. An important symbolic step, the end of the purchases still leaves the Fed far from a normal posture. Its balance sheet has swollen to more than $4 trillion, interest rates remain at zero, and, if anything, recent events have increased the risk the U.S.