If the gradual reductions were halted, it could raise concerns that the Fed has begun to worry about challenges the economy is facing, from a brutal winter that's depressed growth to fears about how Russia's aggression toward Ukraine might slow the global economy.
Fed officials, including Yellen, have signaled their belief that the weakness in U.S. economic data is temporary rather than a sign that the economy is losing momentum.
The Fed and most private economists foresee faster economic growth later this year. Many think the economy, which grew a lackluster 1.9 percent in 2013, will rebound to around 3 percent this year.
"We had a tough start to the year with the winter storms, but it looks like we are starting to pull out of those weather effects," said David Jones, chief economist at DMJ Advisors.
Economists point to several hopeful signs — from a rebound in retail sales to an increase of 175,000 jobs in February despite continued harsh weather.
Even if the economy strengthens and the Fed ends its bond purchases late this year, it will still be stimulating the economy. It has no plans to start selling its enormous portfolio of bonds — a step that would likely send loan rates up. Nor is it likely this year to raise the benchmark short-term rate it controls.
More than five years ago, the Fed cut that rate to a record low near zero, where it's remained since. Most analysts think the Fed will keep its target for short-term rates near zero until late 2015.
Not all economists expect the Fed this week to drop a link between a specific unemployment rate and an eventual rate increase.
"I don't think they will tweak the language," said Brian Bethune, an economics professor at Tuft University. "There is enough wiggle room currently."