US ambassador Georgette Mosbacher said there would be a major boost in the US military presence, in response to requests by Warsaw's rightwing government.

"It will be significant. It passes the hundred mark, the hundreds mark," she told the Financial Times, without specifying a timeline. "I think (the Poles are) going to get most of what they want."

The comments come as Vice President Mike Pence and Secretary of State Mike Pompeo headline a conference in Warsaw on security issues in the Middle East on Wednesday and Thursday that the US is co-hosting with Poland.

Pence and Polish President Andrzej Duda are also expected to finalise a deal on Wednesday allowing Warsaw to buy mobile rocket launchers worth $414 million (365 million euros) from the US.

Poland's government has been pushing for the United States to open a permanent military base on its soil, where American troops are already stationed on a rotational basis as part of NATO operations.

Mosbacher echoed US defence officials who have downplayed any idea of any permanent base.

"But in terms of a presence that is undeniable and a large number of American troops here, that's a given," she said in the FT interview published online.

"The Department of Defense sees (the forces of the 21st century) as . . . more agile, more rotating, rather than where you have physical hospitals and homes and you bring your families," Mosbacher said.

In March last year, Warsaw signed a $4.75 billion contract to purchase a US-made Patriot anti-missile system.

The US leads a multinational NATO battalion in Poland, one of four that the US-led alliance deployed to the region in 2017 to act as tripwires against possible Russian adventurism in the wake of Moscow's 2014 annexation of Crimea from Ukraine.