WASHINGTON — Lawmakers want to make certain the aging A-10 gets at least one more air-power showdown before retiring into the history books.

The Senate is expected to vote this week on a defense bill that requires the Defense Department to submit a side-by-side comparison of the 1970s-era Thunderbolt II and the F-35 Joint Strike Fighter, which is slated to take over many U.S. tactical air power roles including the close-air support that made the A-10 beloved among infantry troops.

Supporters of the legislation, including former A-10 pilot Rep. Martha McSally, R-Ariz., want to see whether the high-tech and expensive F-35 can really fill the role of the A-10, also known as the Warthog, before approving Air Force efforts to retire the battlefield stalwart and its powerful nose cannon. The Pentagon’s Operational Test and Evaluation office said earlier this year that it was planning the fly-off.

The side-by-side test is included in the $619-billion National Defense Authorization Act approved by the House last week. President Barack Obama must sign the bill for it to become law.

“It includes critical language I authored to require a fly-off between the A-10 and the F-35 before a single A-10 can be retired,” McSally said.

McSally has contended the Defense Department has been unclear on how it will manage the future of two of the A-10’s most crucial roles, protecting ground troops on the battlefield and rescuing downed pilots and troops caught in enemy territory.

The Air Force has been angling to retire the A-10 in recent years to save money and clear the way for its variant of the F-35 to come into service. But Congress has objected to the retirement repeatedly, saying the A-10 saves lives on the battlefield, and the NDAA bill again blocks it from phasing out the aircraft over the coming year.

The bill calls for a “comparison test and evaluation that examines the capabilities of the F-35A and A-10C aircraft in conducting close-air support, combat search and rescue, and forward air controller airborne missions.”

The F-35 is billed as the most advanced fighter in the world – it is also the most expensive acquisition program in Defense Department history – and will approach battlefield warfare differently than legacy aircraft such as the A-10. It faces some apparent challenges in the A-10 role because it does not carry the firepower of the Gatling-style nose cannon or the ability to loiter over targets for a long period of time compared to the Warthog.

The director of Operational Test and Evaluation, J. Michael Gilmore, told Congress earlier this year that the test made “common sense” and he was planning the side-by-side comparison of the two aircraft.

“There are a lot of arguments that ensues over which aircraft might have the advantage, the A-10 or the F-35, but that is what the comparison test is meant to show us,” Gilmore told a Senate panel in April.

The NDAA bill calls for Gilmore to report the results to the two Armed Services Committees in Congress and then requires the Defense Department to respond to any deficiencies in the F-35 and submit a plan for maintaining the A-10’s battlefield capabilities.

tritten.travis@stripes.com

Twitter: @Travis_Tritten