The Trump administration’s threat to slap 50 percent tariffs on the European Union and steep tariffs of varying sizes on other critical American trading partners hung in limbo on Thursday after a panel of U.S. federal judges blocked a set of across-the-board charges.

But both trade experts and America’s trading partners around the world greeted the news with caution, not celebration.

Stocks rose internationally as investors hoped the decision, handed down by the U.S. Court of International Trade, might restrain the assault that Washington is waging on world markets. President Trump’s top aides had told the court in recent days that an adverse ruling could weaken the administration’s negotiating position and imperil ongoing talks.

Yet economists pointed out that Mr. Trump could turn to other legal routes to enact across-the-board tariffs. The administration has already filed plans to appeal the decision.

Given that, the court’s move offered only a fragile chance at reprieve for economies like those of Australia, Britain, Canada, the European Union and India. And it all but guaranteed continued chaos.

On the one hand, Washington has been using the threat of sky-high tariffs, enacted unilaterally by the president and without congressional approval, as a cudgel in trade discussions; that might now be a somewhat diminished tool. But on the other, it was not clear whether the reprieve would be sustainable or if the Trump administration would quickly find a way to work around it. The court decision was therefore poised to set off days of scrambling, as the United States tries to reinstate tariffs and global partners watch to see whether that will be possible.