A member of Charlie Company of the U.S. Marines First Division, Eighth regiment, smokes a cigarette in Fallujah, Iraq, Tuesday, Nov. 9, 2004. U.S. forces punched into the center of the insurgent stronghold, overwhelming bands of guerrillas in the street with heavy barrages of fire and searching house to house in a powerful advance on the second day of a major offensive. (AP Photo/Los Angeles Times, Luis Sinco)

The U.S. military is shedding so many troops and weapons it is only “marginally able” to defend the nation and falls short of the Obama administration’s national security strategy, according to a new report by The Heritage Foundation on Tuesday.

“The U.S. military itself is aging. It’s shrinking in size,” said Dakota Wood, a Heritage analyst. “And it’s quickly becoming problematic in terms of being able to address more than one major conflict.”

President Obama’s latest strategy is to size the armed forces pledged in 2014 so that the four military branches have sufficient troops, ships, tanks and aircraft to win a large war, while simultaneously acting to “deny the objectives of — or impose unacceptable costs on — another aggressor in another region.”

In other words, the Quadrennial Defense Review says the military can essentially fight two major conflicts at once. It could defeat an invasion of South Korea by the North, for example, and stop Russia from invading Western Europe or Iran from conquering a Persian Gulf state.

But Heritage’s “2015 Index of U.S. Military Strength” took a look, in detail, at units and weapons, region by region, and came to a different conclusion.

“The U.S. military is rapidly approaching a one-war-capable force,” said Mr. Wood, a former Marine Corps officer and strategic planner. “So [it is] able to handle a major war and then having just a bit of residual capability to handle other minor crises that might pop up. … But it is a far cry from being a two-war force.”

“The consistent decline in funding and the consequent shrinking of the force are putting it under significant pressure,” the report concluded. “The cumulative effect of such factors has resulted in a U.S. military that is marginally able to meet the demands of defending America’s vital national interests.”

The index report is part scorecard, part research tool.

It grades the Army, which is shrinking from 570,000 soldiers to 440,000 or lower, and the Navy, which is failing to achieve a 300-ship force, as only “marginal” in military power. The Air Force’s fleet of fighters and long-range bombers is judged “strong.”

Heritage says the military cannot fight two wars at once.

The report said the Army historically commits 21 brigade dombat teams to one war. Several years ago, that left just 21 more brigades for a second war and none for strategic reserve.

But the problem is more acute. The Army announced in 2013 it may go as low as 33 brigades, far short of the 50 brigades Heritage says are needed.

The Army has been battered by automatic budget cuts known as “sequestration.” A bipartisan budget deal provided some relief last year, but the slashing could come back in 2016 without another agreement.

Gen. Raymond Odierno, Army chief of staff, has said that if the active force is squeezed down to 420,000 soldiers, it could not carry out all global commitments.

The Navy would need 346 ships to carry out two large campaigns, Heritage said, but its fleet is only 284.