The highly-classified program, whose origins go back to the early 1980s, has taken on added importance in the wake of two daring, albeit inconclusive, recent attempts by the US military to kill Iraqi President Saddam Hussein.

On March 20 and April 7, US forces used cruise missiles and bunker-busting bombs against two locations in Baghdad where intelligence indicated Saddam was meeting with his top associates.

In the second attack, it took the US military just 38 minutes, from the moment it received the intelligence tip, to redirect a B-1 bomber loitering over central Iraq, reprogram the weapons systems and level several buildings in a neighborhood where the Iraqi dictator was believed to be hiding.

But both strikes were followed by unconfirmed media reports that Saddam had been missed by just a few minutes.

If US bombers were equipped with the missile now on drawing boards, "he would not have that chance," said US government sources who described the project to AFP on condition of strict confidentiality.

The usually secretive Pentagon gave a hint of the project on March 31, when Deputy Undersecretary of Defense Michael Wynne went before the Senate Subcommittee on Emerging Threats to ask for 150-million-dollar increase in allocations for hypersonic technology that, in his words, would enable the United States to "conduct tactical strikes from a strategic distance" and "deny enemy sanctuary anywhere in the world."

"Technology has progressed to the point where we believe that demonstrations of Mach 12 by 2012 are within reach," he told lawmakers.

Wynne did not publicly disclose whether the requested money was meant for a missile or a plane capable of flying at 12 times the speed of sound, and repeated AFP requests for clarification went unanswered.

But other government sources and outside experts said the project aims to build a hypersonic successor to air- and sea-launched cruise missiles, which currently fly slower than the speed of sound.

"They could be forward deployed on any tactical aircraft," said retired Rear Admiral Stephen Baker, who now works for the Center for Defense Information here. "Certainly, there is the capability of a submarine to go any place in international waters, or a battle group, or a carrier air wing on a carrier."

Baker, who believes the proposed missile could also be used against weapons of mass destruction facilities and enemy missile launch sites, said his former Navy colleagues had informally dubbed it "Fasthawk," after the "Tomahawk," the current staple in the Navy missile arsenal.

The program harks back to the long-forgotten Copper Canyon project launched by former president Ronald Reagan with a lot of fanfare in 1982.

It called for building an aerospace plane that would be zooming at 25 times the speed of sound, covering the distance between Washington and Tokyo in under two hours by flying part of the trip in low orbit.

The aircraft was supposed to use a so-called air-breathing ramjet engine, where thrust is created by water vapor ejected as a result of burning a mix of liquid hydrogen and compressed hot air sucked in from outside into the combustion chamber.

Technical problems and cost overruns eventually forced the US government to move the ambitious plan to the back burner.

But advances in propulsion technology, the availability of new materials and the need to boost US strike capability in the context of the war on terror have prompted US officials to have another look at the old designs, the sources said.

"I think that their conclusion from that exercise was that a Mach 12 suborbital air-breather might be within the realm of possibility," said John Pike, director of GlobalSecurity.org, a Washington area think tank.

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