Lawmakers flanked by veterans and comedian Jon Stewart on Tuesday announced legislation that would deliver care for veterans who developed health problems after they were exposed to open-air pits used to burn trash and waste during overseas wars.

The legislation would declare certain illnesses among combat veterans as linked to toxic burn pits, removing barriers of proof of exposure that advocates have said are too high.

The wars in Afghanistan, Iraq and elsewhere generated enormous amounts of waste, including vehicle parts, lithium-ion batteries, solvents, amputated limbs. U.S. contractors soaked the items in jet fuel and set them ablaze in hundreds of open-air burn pits, some larger than a football field. Veterans advocates say service members exposed to the pits developed cancer and respiratory illnesses, but the U.S. government has said the toxic substances are not conclusively linked to severe health conditions.

In an address at the U.S. Capitol, Stewart blasted lawmakers for not granting broad care and benefits to veterans sickened by burn pits and said the U.S. government has failed service members by setting an “almost impossibly high bar” to prove they were exposed to toxins.

“War after war after war, we treat them as expendable. And when they come home, we’re done with them,” Stewart said later Tuesday in an interview with The Washington Post. “If an enemy did this to us, we’d … bomb them into oblivion. We did it to ourselves and we’re ignoring it.”

As many as 3.5 million service members were exposed to burn pits and toxic chemicals during the first Gulf War through the global war on terrorism, said Sen. Kirsten Gillibrand (D-N.Y.), who proposed the legislation with Rep. Raul Ruiz (D-Calif.). The measure would grant presumption of exposure to veterans with certain conditions and who served in one of 33 countries where troops were deployed after the 9/11 attacks, Gillibrand said.

That would reduce the burden of evidence they must currently provide, she said, such as exposure to specific burn pits and authoritative links to illnesses. That high bar has led to many denials of claims and care, according to Gillibrand and advocates.

VA has maintained there is not enough scientific evidence to conclusively link exposure and chronic health problems and evaluates claims on an individual basis.

Danielle Robinson said her husband, Heath Robinson, developed stage-4 lung cancer after serving with the Ohio National Guard in Iraq, where he lived near burn pits. Doctors said his condition was consistent with toxic exposure, Robinson told reporters. He died in May.

“My husband is dead because America poisoned its soldiers,” Robinson said.

Gillibrand told The Post she and other advocates have tried for years to broaden the scope of benefits and care for sickened veterans, contending with other lawmakers and VA.

“We’ve tried everything else,” Gillibrand said. But the plight of New York first responders, she said, provided a helpful road map.

“We did the epidemiology studies. We know the toxins created on 9/11 were the same at these burn pits,” she said.

The fight for presuming illnesses related to exposure is similar to the plight of Vietnam veterans, who for decades were denied care for exposure to the defoliant Agent Orange. VA now presumes certain conditions are related to exposure based on deployment history rather than relying on the veteran to prove they encountered the chemical at a certain place.

VA spokeswoman Christina Noel said eligibility requirements for VA health care and disability compensation are set by Congress. VA monitors the latest research on burn pits, she said, including a National Academies of Sciences, Engineering, and Medicine study issued Friday.

None of 27 severe illnesses met sufficient criteria to be linked to toxic exposure, the report found, and other conditions such as chronic persistent cough, shortness of breath and wheezing had limited or suggestive links.

Noel said the study found “insufficient evidence” linking respiratory illnesses and combat deployments. The report authors cautioned against such an interpretation, saying incomplete data prevented researchers from drawing definitive conclusions.

A tiny number of compensation claims filed since 2007 — more than 14,000 out of nearly 16 million — are related to burn pits, Noel said. She did not say how many of those were denied.

VA could serve a more proactive role as a veterans health advocate, Stewart said. “But VA is being purposefully obtuse, and they’re purposely misdirecting people as a way of avoiding responsibility … they put veterans on almost a literal trial.”

VA opened a burn pit registry for veterans to document health concerns, and recently noted the 200,000th registrant — a fraction of the overall number that may have been exposed.

“It is past time that veterans exposed to these deadly toxins receive the benefits that they deserve,” said Jeremy Butler, the chief executive of Iraq and Afghanistan Veterans of America, an advocacy group that joined other veterans groups in endorsing the proposed bill.

In Iraq, one notoriously large pit in Balad burned continuously for years, at one point incinerating 147 tons of waste per day, Military Times reported.

Military officials, including an Air Force bioenvironmental engineer in 2006, cautioned that the Balad burn pit posed acute and chronic health risks, Military Times reported.

Stewart, who was also a fierce proponent of extending the health fund for Sept. 11 first responders, said the items burned at Balad and elsewhere included the remnants of firearms.

“The smoking gun,” Stewart said, “is literally smoking guns.”