WASHINGTON — When the two chambers of the U.S. Congress eventually meet to negotiate differences about defense policy, the list of disagreements will be long. Chief among them will be how much money should be authorized for defense in 2013.

The defense authorization bill passed by the House May 18 would add $4 billion to President Barack Obama’s request for defense. Meanwhile, the Senate Armed Services Committee, in its markup of the same bill, would keep defense spending at $631.4 billion.

Both pieces of legislation exceed the spending caps put in place by last summer’s Budget Control Act.

The Senate panel unanimously approved its markup May 24, sending it to the full Senate for consideration. The committee’s chairman, Sen. Carl Levin (D-Mich.), said the bill is slated for debate in June.

“If it doesn’t get done in June, it will get done in July,” he said.

Once the Senate approves a version of the bill, the legislation will move to a conference committee, where members of the two congressional chambers meet to hammer out their differences before sending a final bill to the president to sign into law.

With gridlock on Capitol Hill and presidential politics moving into high gear, it promises to be an uphill battle to get the defense authorization bill passed before November.

The most divisive issue continues to be language concerning the handling of suspected terrorists detained within the United States.

Sen. John McCain (R-Ariz.), ranking member on the Senate Armed Services Committee, said he expects a rigorous debate on the issue when the committee bill moves to the Senate floor.

One area where the House and Senate seem to agree, but where the U.S. Army does not, is new funding for continued production of the M1 Abrams tank in Lima, Ohio.

The Senate Armed Services Committee recommends adding money to the Army’s budget request to keep the production line open. Army leaders, including the service’s chief of staff, Gen. Ray Odierno, have testified that the Army does not need new tanks and that the service would like to temporarily shut down the Ohio plant until tank upgrades are needed in a few years.

House lawmakers provided similar unrequested funding for Army combat vehicles.

The Senate committee has rejected the Air Force’s proposed cuts to the Air National Guard, and instead recommends fully funding the Guard’s equipment and personnel needs in 2013.

After the Air Force released its budget request in February, a fierce battle has been fought by Air National Guard advocates and the country’s governors to undo the service’s proposed cuts, which they say disproportionately target the Guard.

“Never underestimate the influence of the National Guard,” McCain said during a May 24 press conference.

To increase funding to the National Guard and in other areas, the committee recommended roughly 150 changes to the president’s request. Levin said he and other lawmakers remain unconvinced by the Air Force’s analysis for the Air National Guard reductions.

“There was a broad feeling that the Air Force did not have solid analysis behind its reductions,” Levin said. When the committee asked the Air Force for more information, it either did not get it or what was provided was unconvincing, he said.

To address these concerns, the committee recommends Congress establish a national commission to make recommendations on future force structure decisions within the Air Force.

These recommendations would be due March 31, 2013, Levin said. They would not be binding, but would be available for the congressional defense committees to include in legislation.

“We want to try to prevent this kind of decision from being made in the future with as little care as this one was made,” Levin said.

He said he would like to see force structure cuts that are based in factual analysis and that are also more proportional.

The Air Force’s budget proposal included a cut of 5,100 Guardsmen.

Other measures in the bill include capping executive pay that is reimbursable under defense contracts at $237,000.

The bill would require the Pentagon to reduce its civilian personnel, which McCain said had grown by 16 percent since 2007. The bill would require the defense secretary to reduce civilian staff members by 5 percent over five years, saving more than $5 billion, McCain said. He described the proposal as “one of the most important things” the committee did in its markup.

Following similar steps by House lawmakers, the Senate panel recommended increasing funding for the Israeli rocket defense system known as Iron Dome by $210 million.