A new US-Russian arms reduction treaty will be beneficial for US missile defense capacity, the head of the US Missile Defense Agency told congressional critics of the agreement on Thursday.

Republicans lawmakers have criticized the successor START (Strategic Arms Reduction Treaty) deal, signed amid much fanfare in Prague last week by President Barack Obama and his Russian counterpart Dmitry Medvedev.

They argue it will inhibit development of adequate US anti-missile defense systems, but Missile Defense Agency (MDA) head Lieutenant General Patrick O'Reilly rejected that claim.

"The new START treaty actually reduces constraints on the development of the missile defense program," he told the House of Representatives subcommittee on strategic forces.

O'Reilly said the agreement would allow previously prohibited tests for the development of anti-missile defense systems.

"Our targets will no longer be subject to START constraints, which limited our use of air-to-surface and waterborne launches of targets which are essential for a cost-effective testing of missile defense interceptor against medium-range and intermediate-range ballistic missiles in the Pacific region," he said.

The new treaty must be ratified by the Senate, though not the House of Representatives, to take effect.

Ratification requires yes votes from at least 67 of the 100 senators, meaning support from several Republican lawmakers must be secured.

O'Reilly's comments came during a hearing on the proposed 2011 budget beginning October, which includes a request for 9.9 billion dollars for missile defense, up 670,000 million dollars from last year.