The US will send 1,000 more troops to Poland, President Donald Trump said during a press conference with Polish President Andrzej Duda.
President Trump said the troop would be taken from the 52,000-strong American contingent in Germany drones and other military equipment.
However, he missed the commitment to a permanent US base in the country.
According to bids from Warsaw, $ 2 billion (£ 1.57 billion) was spent on building such.
] The base could be called Fort Trump, joked President Duda during his visit to the White House on Wednesday.
President Trump said that America was "very interested" in the idea, but hesitates to commit to a permanent institution – which is likely to be one Russia's reaction.
"I do not talk about permanence or not durability," he told reporters, The visit of Mr. Duda – the second in less than a year – celebrated the 20th anniversary of Poland's membership in NATO and the 30th anniversary of the fall of communism in the country.
Speaking to reporters, Mr. Duda thanked Mr. Trump for his "extreme friendliness towards Poland and his perfect understanding of Polish affairs".
After leaving Washington, the Polish president is scheduled to travel to Texas, Nevada and California to hold talks on energy and technology.
Last year, the Warsaw government called on Americans to establish a permanent military base in Poland to take in a division (several thousand) of US troops.
The idea was quickly called "Fort Trump". But there were problems.
Who would pay? Up to $ 2 billion was offered by Warsaw, but this would only cover the initial setup of the base.
Where would the troops come from? It would be very costly to close them off from the US. A transfer of Germany or Italy could affect the cohesion of the Alliance.
Above all, a permanent basis could violate the 1997 agreement between NATO and Russia.
What happened is a fudge. Fewer troops than requested, in exchange. This is seen by US commanders as an increase in readiness.
However, these rotation troops will help build Poland's military infrastructure so that it can accommodate far more soldiers if needed in the future.
What have the US and Poland agreed on?
The two heads of state and government have signed a joint declaration on defense cooperation by American troops "temporarily stationed on a rotation basis."
However, in a later poll by reporters, Trump said, "You're talking about 2,000 Soldiers. "
Talking to the BBC, a United States Secretary of State The Department of Defense could not confirm how many employees would be sent to Poland under the new agreement.
It is also unclear who will pay the costs