What happens next on tariffs is a critical wild card for the central bank. While tensions have shown recent signs of easing, how they will end is anyone’s guess. Barring a last-minute delay, another round of tariffs on $160 billion worth of Chinese goods is to go into effect on Sunday, at which point the United States will have imposed levies on nearly every shoe, laptop and bicycle imported from China.

But for now, growth looks solid — and sustainable.

All 17 Fed officials were comfortable leaving rates unchanged this month, and only four see higher rates in 2020, based on the economic projections, down from nine when the Fed released its last set of quarterly projections in September.

While the Fed is usually more eager to raise interest rates when unemployment is very low, that view has evolved dramatically over the course of the expansion.

Lawmakers have given the central bank two goals: achieving and maintaining stable inflation and maximum employment. Fed officials adjust interest rates to either speed or slow the economy in a quest to accomplish those targets.

They have historically seen the twin tasks as a sort of trade-off. Low unemployment is usually expected to spur faster wages, which then feed into higher prices.

But joblessness has been hovering near a 50-year low for the past year and a half, and wages are climbing only moderately while upward pressures on prices are soft.

“I like to say that the labor market is strong; I don’t really want to say that it’s tight,” Mr. Powell said. “To call it hot, you’d want to see heat. You’d want to see higher wages.”