WASHINGTON — A former director of the U.S. Missile Defense Agency (MDA) on March 5 prescribed a handful of changes the Pentagon should make to improve its European missile defense plans and ensure the United States’ strategic missile shield remains viable in the long term.

The MDA would be better able to pay for continued development of its missile defense systems if the Army and Navy started paying the bill for their operational interceptors, retired Air Force Lt. Gen. Henry “Trey” Obering said at an event here organized by the Aerospace Industries Association.

Obering, who led the agency from 2004 through 2008, helped craft a plan for European missile defense that was announced by the administration of then-U.S. President George W. Bush in 2006. The plan called for placing 10 long-range interceptors in Poland and a fixed-site midcourse tracking radar in the Czech Republic.

The administration of U.S. President Barack Obama in September 2009 unveiled a revised approach to European missile defense based on land- and sea-based variants of the Aegis Ballistic Missile Defense system and Standard Missile (SM)-3 interceptors. For the first increment of the so-called Phased Adaptive Approach, a U.S. Aegis ship was deployed in March to the Mediterranean Sea. The Pentagon also plans to deploy an AN/TPY-2 mobile X-band radar to Southeastern Europe this year, but it has not announced which nation will host it.

The United States should reconsider placing a midcourse tracking radar in Europe to improve the effectiveness of the Phased Adaptive Approach, said Obering, now a senior vice president at Booz Allen Hamilton of McLean, Va. Russia opposed the Bush-era plan for European missile defense in part out of concerns that the radar site would be able to peer far into Russian airspace. But that concern was adequately addressed in NATO Russian Council meetings, Obering said.

“The radar is physics-based, and there’s a beam height of that radar, so if you extrapolate that beam from its position in the Czech Republic out to Russian territory, it would be about 750 kilometers in space,” Obering said. “So there’s no ability to look into Russian airspace with that radar.”

The Pentagon also lacks an adequate strategy to hedge against delays in the development of future elements of the Phased Adaptive Approach, Obering said. Navy Aegis ships today carry SM-3 Block 1A interceptors built by Raytheon Missile Systems of Tucson, Ariz. By 2015, the Pentagon plans to deploy the more capable SM-3 Block 1B interceptors on Aegis ships and at ground sites in Romania. The larger SM-3 Block 2A interceptor would be available in 2018.

The SM-3 Block 1B has encountered difficulties with its new divert and attitude control system, and its first flight test slipped from 2009 to later this year, Obering said. He cautioned that further delays for both new interceptors are likely in the next few years.

“Any new program is going to have issues they have to deal with,” he said. “What’s a little disturbing to me is there was a lot of painting the SM-3 Block 1B program as proven and reliable and just another flight test of the current version, and it’s not.”

As a backup plan, the MDA continues to develop and test the two-stage ground-based interceptor that was previously planned for deployment in Poland. But the agency must further flesh out its hedging strategy, Obering said. One possible option would be to prepare the two-stage interceptors for use on a transportable launcher platform, he said.

Obering also said the MDA is not providing enough resources for the Ground-based Midcourse Defense system that is the United States’ only defense from long-range missiles. The five-year spending blueprint the MDA submitted to Congress in February contains some $1 billion less for the program than the previous year’s budget submission.

“I’m very concerned that we don’t have sufficient resources in the [Ground-based Midcourse Defense] program to keep that on track and viable,” Obering said.

The MDA could increase its investments in these and other areas such as directed energy research and development if the services would start buying their own interceptors, he said.

“The Missile Defense Agency was never meant to be an operational or procurement agency in terms of force structure,” Obering said. “It was not up to me to determine how many of these we buy … and where they go.”