Speaking to public broadcaster Polish Radio, Bosacki said Foreign Minister Radosław Sikorski had been discussing the proposal with US officials for months and that further talks were planned in the coming weeks.
Bosacki said the outcome would depend primarily on two factors: whether the United States decides to accept Poland's offer to build a permanent base, and the scale of an expected restructuring of the US military presence in Europe.
"The Americans have made it clear to their allies that there will most likely be an overall reduction of US forces in Europe," Bosacki said.
"The key question is whether, as part of that reduction, it will still be possible to establish a large permanent US base in Poland," he added. "We are making that case to the Americans, and we are convinced that some of them find our arguments persuasive."
Bosacki said he expected a decision "probably in the autumn" and voiced confidence that the chances of securing the base were "quite high," citing both strategic considerations and "the current state of Polish-US relations."
If approved, the base would most likely be built in western Poland, he said.
Bosacki noted that constructing a permanent US military installation would be a major logistical undertaking.
"If such a decision is made in the coming months, then within two or three years it would be necessary to build what is effectively a small town—a permanent American military base with the infrastructure needed to support troops and their families," he said.
Asked about financing, Bosacki said Poland would cover the full cost under an existing agreement between Warsaw and Washington.
Poland has long sought to expand the presence of US forces on its soil. American troops are currently stationed in the country on a rotational basis, with units deployed for limited periods before being replaced.
In June, Defence Minister Władysław Kosiniak-Kamysz said the Pentagon was open to Poland's proposal for permanently stationing US forces, while cautioning that any decision would depend on the details of a future agreement.
Later that month, he said talks with Washington had entered a new phase and that the Pentagon's global force posture review would help determine future US troop deployments.
In mid-July, Deputy Defence Minister Cezary Tomczyk announced the creation of a negotiating team within the defence ministry to conduct talks with the United States on establishing a permanent military base in Poland.
He identified areas around the cities of Poznań and Wrocław as potential locations for a permanent US base, citing long-standing NATO infrastructure investment there.
Bartosz Grodecki, head of the Polish president's National Security Bureau (BBN), has said that the US willingness to discuss the proposal should be translated into concrete steps to conclude negotiations as quickly as possible.
About 10,000 US troops are stationed in Poland, most serving on a rotational basis, according to officials.
The Pentagon announced in May plans to withdraw 5,000 troops from Germany and later scrapped a planned rotational deployment of 4,000 troops to Poland as part of a broader reduction of the US military footprint in Europe.
Days later, however, US President Donald Trump said he intended to send an additional 5,000 troops to Poland. That announcement followed intensive lobbying by Warsaw and bipartisan pressure in Washington over the future of the US military presence in Europe.
Kosiniak-Kamysz said last month that Hegseth had responded positively to Poland's proposal to establish a permanent US military base in the country.
Polish President Karol Nawrocki said earlier this month that discussions on a permanent American presence were progressing and that the political conditions for such an agreement were in place.