WASHINGTON — The United States and the European Union stepped back from the brink of a trade war Wednesday, after President Trump said the Europeans agreed to work toward lower tariffs and other trade barriers and to buy billions of dollars of US soybeans and natural gas.

The surprise announcement, made by Trump and the president of the European Commission, Jean-Claude Juncker, defused, for the moment, a trade battle that began with Trump’s tariffs on steel and aluminum exports and threatened to escalate to its automobiles.

“We’re starting the negotiation right now, but we know very much where it’s going,’’ Trump said, standing next to Juncker at a hastily scheduled appearance in the White House Rose Garden.

Juncker said, “I had the intention to make a deal today, and we have made a deal today.’’

The two sides, he said, had agreed to hold off on further tariffs and work toward dropping the existing ones on steel and aluminum, while they tried to hammer out a deal to eliminate tariffs, nontariff barriers, and subsidies on industrial goods, excluding autos.

It was hard to say, given Trump’s bluster and unpredictable negotiating style, if the agreement was a genuine truce or merely a lull in a conflict that could flare again. Twice, Trump’s aides have negotiated potential deals with China, only to have him reject them and impose further tariffs. Cutting these trade barriers to zero would be an extraordinarily complex political challenge on both sides of the Atlantic.

And Trump stepped back from punitive tariff threats for some relatively minor European concessions: the purchase of soybeans to make up for a steep falloff of buying by China and the promise to purchase liquefied natural gas once the United States builds more LNG export terminals, which are far away. For weeks, the president has portrayed the European Union as fleecing America with unfair trade, but he put away his saber as farm state Republicans were begging for relief.

“I think it’s helpful that they made some progress today with the European Union, and I think we really emphasized that we need to keep the momentum up and get the deals as soon as we can,’’ said Senator John Hoeven, Republican of North Dakota, who was at the White House for the announcement.

Europe’s pledge to buy more natural gas gives Trump a talking point with Russia, after he vowed to compete for orders in Europe, where Russia is the largest supplier, though the lack of natural gas terminals means that this windfall is years in the future.

Still, Trump called it “a new phase in the relationship between the United States and the European Union,’’ a striking change in tone from his recent trip to Europe, when he referred to the European Union as a “foe’’ and criticized its most important member, Germany, for its dependence on Russian gas.

The Trump administration has already imposed billions of dollars of tariffs on the EU for what it has labeled unfair trade practices, raising costs for companies and consumers and roiling a traditionally close alliance. Trump’s threat to go after automobiles particularly rattled the Germans, who export millions of BMWs and Mercedes-Benzes to the United States but also produce millions at US factories, mainly in the South, an electoral stronghold of the president.

Juncker was dispatched to Washington this week along with other European officials as part of a last-ditch effort to halt those tariffs. A former prime minister of Luxembourg known for his informal manner and occasional gaffes, Juncker has forged a good rapport with Trump, and the two men appeared at ease on Wednesday.

“Disaster avoided,’’ said Bart Oosterveld, the director of the global business and economics program at the Atlantic Council. “Earlier today, our highest hopes were for a truce, and this is kind of like a truce.’’

Fred Bergsten, senior fellow and director emeritus of the Peterson Institute of International Economics, said an agreement with Europe would allow Trump to focus on China. But he said that the deal seemed to have an “eerie similarity’’ to one with China earlier this year, shortly before Treasury Secretary Steven Mnuchin announced that the trade war was “on hold.’’

“We have seen something like this movie on the other major trade front only a couple of months ago, and I would just hope that it would not play out in the same way, which at the moment seems to be a stalemate with China,’’ Bergsten said.

Trump did not promise to remove the tariffs on shipments of steel and aluminum from Europe, and the Europeans did not promise to lift their retaliatory tariffs. But he said that the tariff issues would “get resolved as part of what we’re doing.’’

Juncker had called the US tariffs and the cycle of retaliation they had invoked “basically a stupid process,’’ saying the Europeans would be forced to respond in kind.

European officials have been worrying that the tit-for-tat trade actions were merely locking Europe and the United States into a destructive cycle of relations that will leave consumers and companies on both sides of the Atlantic worse off.

Trump has lambasted the EU for charging a 10 percent tariff on imported cars, running a trade surplus with the United States, and maintaining barriers to US farm products, saying earlier this month that the Europeans were “possibly as bad as China’’ when it comes to trade.

Economists have challenged these claims. They counter that average tariffs across both nations are extremely low, and that the US trade deficit is more a function of broader economic factors, including the US savings rate, than any specific tariffs. Even in the realm of automobiles, the United States charges only a 2.5 percent tariff on imported cars, but it has a 25 percent tariff on foreign trucks and maintains higher levies on many other products.

“Tariffs are low throughout the industrialized world,’’ said Justin Wolfers, an economist at the University of Michigan. “Basically, if you said there’s no more tariffs to reduce, you would barely be wrong.’’

In a briefing Tuesday, a senior European official said that Juncker was prepared to discuss two options to revive the trading relationship — either an agreement that would involve many of the world’s biggest auto exporters slashing car tariffs together, or a trade deal between Europe and the United States that would be limited to certain products.

The European Union has struggled to figure out what exactly the United States would like to gain through talks and whether the Trump administration is negotiating in good faith, the senior official said.

White House officials have described their tariffs as a negotiating tool to secure better trade agreements. But meanwhile, the Trump administration has shelved previous talks with Europe over a broader trade agreement, called the Transatlantic Trade and Investment Partnership.