WASHINGTON — A photo of a smiling Iranian President Mahmoud Ahmadinejad peeked out from behind the clutch of Iraq war veterans that gathered on Capitol Hill recently to press Congress to pass climate change legislation.

“I found myself not taking out the terrorists, not securing Iraq, but protecting oil,” said retired Marine Corps sniper Matt Victoriano, who served two tours of duty in Iraq in 2003 and 2004. He came to Washington with Operation Free, a project that takes veterans around the country to talk about the connection between national security, energy and climate change.

They point to the billions of American dollars spent annually on fossil fuels from hostile nations, the vulnerability that oil dependence creates for the military and the threat the conflict sparked by dwindling water supplies could spread U.S. forces thin.

“There is no greater threat to our national security than our dependence on oil,” Victoriano said as he presented Sen. John Kerry,D-Mass., with a digital counter ticking the millions of dollars the United States spends daily on Iranian oil.

With polls indicating the American public is losing confidence in the science of climate change, proponents of emissions-capping energy legislation, such as the sweeping energy-reform bill unveiled by Sens. Kerry and Joe Lieberman, I-Conn., on Wednesday, are shifting their argument to one of national security.

“People are either on one side or the other on the science, and it seems to me that arguing that can be a little futile,” said Phyllis Cuttino, who leads the Pew Charitable Trust’s climate change and energy programs. Over the past year she has traveled around the country with leaders from the defense community to talk about the security risks posed by climate change.

“We have found that this argument is one that people really haven’t considered before,” Cuttino said.

Military officials are concerned not only with America’s dependence on foreign oil, but also with the potentially destabilizing effects of drought, sea-level rise and reduced access to fresh water brought about by climate change.

In February, the Department of Defense released a major policy report on defense strategy that called climate change a “threat multiplier” with the potential to accelerate conflict. Security-focused think tanks also have published a flurry of studies enumerating the risks climate change poses in fragile regions of Africa, the Middle East and southeast Asia.

“We think that [countering climate change] is one of America’s big strategic imperatives – to reduce our reliance on foreign sources of fossil energy, to make us better war-fighters, to get us more down the road to energy independence,” Navy Secretary Ray Mabus told reporters recently.

Posing climate change as a security challenge puts military leaders, who traditionally enjoy a broad range of public support, at the forefront of the public debate, rather than scientists, who have come under scrutiny for mistakes in a U.N. report.

“America respects the military, trusts the military, and when they decide something is in the country’s best interest, Americans by and large support it,” said retired Sen. John Warner. In 2008, he and then-Sen. Hillary Clinton, D-N.Y., drafted legislation requiring the Defense Department to consider the potential effects of climate change on future military missions. Since his retirement last year, Warner has traveled with Cuttino’s group.

“We’re giving people more facts and food for thought, but the mind change on this is going to take some time,” Warner said.

Supporters of the recent Senate measure are hoping the argument will win votes. House Democrats facing fire for their support of last year’s reform bill are hoping the argument will give them cover in the November elections.

Rep. John Boccieri, a freshman Democrat who represents a coal-dependent region of Ohio, is one such member. When his vote made him a target for Republicans and the Ohio Coal Association, he defended it as one in favor of American safety.

“Look, I’m not a scientist,” said Boccieri, who served in Iraq in 2003 as a National Guardsman. “But when the DOD and CIA say we need to elevate this to an area of national security, then we need to pay attention.”

Boccieri has help in making this argument to voters. VoteVets, a lobbying group of progressive veterans, says it has poured about $4 million into an ad campaign that is running in Ohio and a handful of other swing states. In the ads, Iraq war veteran Christopher Miller, who was awarded a Purple Heart as a result of the explosion of an improvised explosive device, draws a clear line between the weapon and the billions of American dollars spent on Iranian oil.

“This is the heart of the issue, this is the bottom line,” said VoteVets co-founder Jon Soltz. “With these ads we really worked to explain to people how keeping the price of oil high gets more money to our enemies.”

Soltz touts polling by his group that shows 79 percent of Iraq and Afghanistan veterans see dependence on foreign oil as a threat to national security. Political pollsters, though, say that this hasn’t yet translated to public support for climate legislation.

“In swing districts, this campaign really comes down to the economy and jobs,” said David Wasserman, who analyzes House races for the Cook Political Report. “Selling climate change as a national security issue strikes many voters as a distraction or something that Al Gore would say.”