WASHINGTON — The Federal Reserve signaled Wednesday that it plans to begin raising its benchmark interest rate as soon as March, a key step in reversing its pandemic-era low-rate policies that have fueled hiring and growth but also escalated inflation. With high inflation squeezing consumers and businesses and unemployment falling steadily, the Fed also said it would phase out its monthly bond purchases, which have been intended to lower longer-term rates, in March. The Fed’s actions are sure to make a wide range of borrowing — from mortgages and credit cards to auto loans and corporate credit — costlier over time.