Central bankers are hoping that both Congress and state and local authorities will step up come the next recession, helping to offset any economic pain. Monetary policy remains a powerful tool for fighting downturns — and officials plan to use mass bond-buying and promises to keep rates low for longer to make up for their lost room to cut rates. But central bankers could run out of the ammunition they need to quickly return the economy to health.

The Fed has long used the federal funds rate as its primary tool for guiding the economy, and it is now set in a range of 1.5 percent to 1.75 percent. It was above 5 percent heading into the 2007-09 recession.

“Long-term interest rates are likely to be much lower going into the next downturn than they were going into any recession in the past 75 years,” a set of top economists wrote in a paper prepared for the conference. “This will clearly limit the potential for old and new monetary policy tools to ease financial conditions and bolster economic outcomes.”

The Fed chair, Jerome H. Powell, often tells lawmakers that the Fed will need their help going forward. During testimony last week, he said that “it would be important for fiscal policy to help support the economy if it weakens.”

But Ms. Brainard’s implication that Congress should be thinking about how to make fiscal tools more automatic goes a bit further. The idea that Congress could pre-commit to taxing or spending policies that would kick in as soon as the economy started to slow has increasingly been a centerpiece of Fed and academic economic research.