In prepared remarks released before the hearing, Powell contrasted the Fed's "baseline outlook" of continued USA growth against a considerable set of risks - including persistently weak inflation, a slowdown in other major economies, and a downturn in business investment driven by trade risks.
Some businesses, particularly in manufacturing, have pulled back on spending and hiring because of greater uncertainty about US trade disputes, Fed officials said, according to minutes of the June 18-19 meeting released Wednesday.
Neither Barkin nor Bostic ruled out supporting a rate cut, which, according to minutes of the Fed's June meeting, has drawn support for a variety of different reasons - both the global tensions Powell has focused upon, as well as weak inflation and a sense that the Fed had unintentionally set policy too tight with its four interest rate increases a year ago.
Powell is scheduled to appear before the US House of Representatives Financial Services Committee at 10am EDT (1400 GMT) as part of his semi-annual monetary policy testimony to Congress.
The Fed has kept its current benchmark overnight interest rate in a range of between 2.25% and 2.50% since December.
The minutes showed widespread concern that the economy is losing steam. A cut could lift home and auto sales by lower the borrowing costs for major purchases.
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Reducing rates at this point would be similar to the Fed's efforts in the mid-1990s to nurse along a lengthy recovery rather than respond to a looming downturn, and "there's no immediate need to move", Philadelphia Fed President Patrick Harker said on Tuesday.
As Trump tied the threatened tariffs, which would have hit one of the world's most integrated supply chains, to non-economic demands about immigration, investors over two days knocked about a quarter of a percentage point from the federal funds rate expected at the end of 2019.
Investors expect that cut with near 100% certainty.
Some Fed officials, however, said that while they expected fewer rate hikes than they had in the past, "there was not yet a strong case for a rate cut from current levels".
At its June 18-19 meeting, many policymakers expressed the view that stimulus would be needed soon, according to the minutes from that meeting released on Wednesday.
"Manufacturing, trade and investment are weak all around the world".
"We anticipate that Powell will stick with a cautious line", they wrote.