When Democrats meet Republicans on the field of battle over missile defense, Robert M. Gates will be providing them cover from up above.

The Defense secretary’s wholesale plan to reshape the military, as shown in the Obama administration’s budget proposal, includes big changes to missile defense, namely terminating or gutting several high-technology systems and returning the enterprise, which received more than $9 billion last year, to its research roots.

The proposal is outlined in the fiscal 2010 defense budget request and the administration is using Gates’ credibility, his Republican bona fides, and his history as a supporter of missile defense to defend the proposed changes, experts say.

“They’re clearly relying on Secretary Gates and his credibility,” said Tom Donnelly, a resident fellow at the American Enterprise Institute. “I’m not sure a Democratic secretary of Defense could do this as successfully.”

By presenting missile defense as part of an overall defense budget that is leveling off, Gates is forcing lawmakers to cut other prized programs if they want to advocate for increased funding for missile defense, said John Isaacs, executive director of the Council for a Livable World.

“Gates was very shrewd,” said Isaacs, “The squeeze has been put on the pro-missile defense forces, making it more difficult to restore funds.”

“We are not cutting missile defense capabilities,” David Altwegg, executive director of the Missile Defense Agency told reporters May 7. “Rather, we are reshaping and redirecting our technologies to improve and enhance our capabilities now and in the future.”

Gates stood behind his record to defend the changes at a May 14 Senate Armed Services Committee hearing.

“I’m a strong defender and proponent of missile defense,” he told senators. “But I want to spend the dollars on missile defense both on R&D and operationally where they will do us the most good.”

Along those lines, President Obama and Gates are proposing increased funding for near-term missile defense elements focused on theater defense and based on more proven technologies.

Democrats have been proposing similar changes for missile defense since reassuming power in 2007 but Republicans, aided by some Senate Democrats, were able to stave off most of those initiatives.

But with the administration and Gates working in tandem, many Democrats feel confident they can preserve the president’s changes to the program in the upcoming defense authorization and appropriations bills.

“There’s no question that the changes will be easier to sustain because of the change in the balance of power in the House and Senate,” said John M. Spratt Jr. , a member of the House Armed Services Strategic Forces Subcommittee.

Despite what looks like an uphill climb, Republicans aren’t giving up the fight to increase overall missile defense funding and save targeted components.

Rep. Michael R. Turner of Ohio, the ranking Republican on the House Armed Services Strategic Forces Subcommittee, said the GOP intends to use amendments and parliamentary procedures to boost the MDA’s budget, which would receive $7.8 billion under the president’s plan.

They also will use missile defense cuts to criticize the White House for increasing the budget for non-defense programs.

“This isn’t an administration that’s been concerned about spending,” said Turner.

In the end, experts warn that even if Obama and Gates are able to sustain most of their proposed missile defense changes through the legislative process, supporters of missile defense components could preserve small parts on which to fight another day.

“Ultimately, Gates should prevail largely if not entirely on his missile defense proposals, but it won’t be a slam dunk,” said Isaacs. “It’s very hard to kill a program and put a stake in its heart so it never lives again.”