The Pentagon cancelled a rotation of around 4,000 troops on 13 May.
President Donald Trump reversed the decision days later, announcing he would send 5,000 troops to Poland instead, but the cable warned the political damage may be hard to undo.
The document, obtained by US news website Politico and signed by US Ambassador Tom Rose, was sent to Secretary of State Marco Rubio's office.
It described Polish reactions in the intervening period as "disappointment", "bewilderment" and "genuine alarm".
"The dominant emotional reaction is one of perceived betrayal," it stated, noting that Trump had repeatedly praised Poland as America's most reliable and committed ally in Europe.
Warsaw has increased its defence spending more than any other NATO ally in recent years, buying tens of billions of dollars' worth of US-made weaponry and paying to host around 10,000 American troops on its soil.
The cable also pointed to inconsistent messaging stretching back to the Biden administration, which had approved the rotations after Russia's full-scale invasion of Ukraine in 2022.
"Temporary rotational presence gradually became understood inside Poland as a semi-permanent security guarantee, something we did precious little to counter," it said.
The cable warned the fallout risked "fuelling pressure to move away from American defence systems, accelerating momentum behind EU defence integration at America's expense, and driving anti-American political and media narratives across the region".
Among the suggestions Ambassador Rose offered to limit the damage was replacing the large armoured rotation with a "smaller but clearly enduring" US presence focused on command and control, logistics, air defence and rapid reinforcement.
Such an arrangement, the cable noted, would also "save millions of dollars" compared with rotating an armoured brigade every nine months.
According to Politico, the incident also hurt Polish President Karol Nawrocki, a political ally of Trump.
His senior aide, Marcin Przydacz, described the situation as "chaotic communication" in Washington, calling it "a bit of misunderstanding within the Pentagon".
(ał)
Source: PAP, Politico