Congressional auditors are advising the Pentagon to redesign and successfully test a version of the Standard Missile 3 before allowing the interceptor to be produced.

The recommendation could prove controversial at the Defense Department, especially because European deployment of the antimissile technology in question is planned for next year.

The Tuesday report by the Government Accountability Office raised concerns that the Pentagon's Missile Defense Agency is poised to approve production of the Standard Missile 3 Block 1B interceptor, despite not knowing what caused one of the missiles to fail during a September 2013 intercept test.

The congressional watchdog advised the agency to await full-production approval for the interceptor until both a determination is made on whether changes to the system's hardware or software are necessary, and any such modifications have been proven through testing that "demonstrates that the redesigned missile is effective and suitable."

The SM-3 Block 1B is designed to destroy short- and medium-range ballistic missiles. The interceptor is planned for fielding beginning in 2015 on U.S. warships home-ported in Spain and at a site in Romania, as part of Washington's contribution to NATO missile defense.

A timely deployment of the weapon has taken on greater urgency for some congressional lawmakers, in light of recent military actions by Russia in Ukraine.

Three successful intercept trials of the weapon were carried out in 2013. It was during a salvo test in September that the failure of a launched Block 1B interceptor occurred.

"A failure review is ongoing to determine the root cause of the failure and may result in design changes to a component common to the [earlier-generation] SM-3 Block 1A," the 49-page report reads. "Effects on production remain unclear."

Christina Chaplain, the GAO head of acquisition and sourcing management, in a Wednesday appearance before the Senate, observed that "MDA continues to procure new 1B interceptors while it investigates the cause of the failure."

The Pentagon's practice of buying antimissile systems before testing on them is complete is putting substantial taxpayer dollars at risk, she said in her in written testimony submitted to the Senate Armed Services Subcommittee on Strategic Forces.

The Missile Defense Agency has repeatedly employed a "high-risk" strategy of "committing to product development before [program] requirements are understood and technologies are mature," Chaplain said.

The agency's schedule for acquiring new antimissile systems frequently overlaps production with technology development, according to the report produced by Chaplain's office. Such a strategy "often results in performance shortfalls, unexpected cost increases, schedule delays, and test problems," the document states.

At the same time, the Pentagon continues to experience performance challenges with its Ground Based Interceptor, which is meant to defend the United States against a possible intercontinental ballistic missile attack. The GBI missile is already deployed at sites in California and Alaska, and there are plans to augment the latter site with 14 additional interceptors in 2017.

Those new interceptor acquisition plans have been called into question by the Government Accountability Office and others, who point out that the missile has not had a successful test intercept since 2008, with three more recent attempts having failed.

Estimated costs for fixes to the interceptor and for recovering lost ground from the multiple test failures total approximately $1.3 billion, Chaplain said on Wednesday.

"We do believe those costs could have been avoided," had the Pentagon observed a so-called "fly before you buy" approach, she said.

The Defense Department has long insisted that its policy is to purchase only those weapons that have been appropriately vetted through testing.