WASHINGTON — The U.S. Defense Department’s controversial Conventional Prompt Global Strike (CPGS) concept will not be a conventionally tipped ICBM after all, Pentagon officials said.

The Defense Department’s civilian leaders finally weighed in after a series of seemingly contradictory statements from U.S. Air Force leaders.

“Current CPGS activities develop and demonstrate ‘boost-glide’ technologies. Boost-glide concepts use rocket-boosted payload delivery vehicles that glide at hypersonic speeds in the atmosphere for most of their flight path, giving them a distinctly non-ballistic flight trajectory,” a Pentagon spokeswoman, Air Force Lt. Col. Melinda Morgan, wrote in an e-mailed statement Mach 10.

The nonballistic trajectory, which is distinctly different from the flight path of an ICBM, would prevent foreign powers from mistaking the weapon for an incoming nuclear attack, she said.

“Currently, the [Department of Defense] has no plans to replace nuclear weapons on ICBMs or [submarine-launched ballistic missiles] with conventional weapons that fly ballistic trajectories,” Morgan said.

Despite research into the weapon, the Department of Defense has not decided to buy the CPGS for operational use.

“While no decisions have been made regarding specific system concepts or acquisition programs for deployment, these boost-glide technologies could be applied to a broad range of CPGS system configurations,” Morgan said.

On March 2, the service’s top uniformed officer said an ICBM with a conventional explosive warhead, along with a hypersonic glider, were options for the service’s CPGS portion of its nascent Long Range Strike family of systems.

“We don’t know yet. The less challenging solution to that demand signal clearly is a conventional ICBM application or [submarine-launched ballistic missile]. There are complications with that, which are pretty self-evident,” Gen. Norton Schwartz, the Air Force chief of staff, said at a conference hosted by Credit Suisse.

“The hypervelocity test vehicle is another potential solution, which is much less mature, obviously,” Schwartz said. “We have another test coming up. We’ll see how that one goes.”

Loren Thompson, chief operating officer at the Lexington Institute in Arlington, Va., agreed that a hypersonic boost-glide weapon would be much less mature. It would take a lot of money and developmental work to build and test such a weapon, he said, but it would be far safer because it would not be mistaken for a nuclear-tipped missile.

“Unless they have something far advanced in the black world, that would take quite a while to develop,” Thompson said.

Schwartz’s comments came a day after Stephen Walker, the Air Force’s science and technology director, told a congressional hearing that a conventionally tipped ICBM was, indeed, an option.

However, that followed conflicting statements by other Air Force generals.

On Feb. 26, Maj. Gen. David Scott, who directs the Air Force’s operational requirements, said, “We have no plans for conventionally armed sea-based missiles such as Conventional Trident Modification or conventionally armed ICBMs. Our focus is on boost-glide capabilities, including the Hypersonic Technology Vehicle concept.”

That followed a Feb. 17 interview in which Scott said, “Conventional Prompt Global Strike, which is the conventional Trident missile and it’s the conventional strike missile; it’s the things that we in the Air Force are working very closely with, with the hypersonic test vehicle that you’ve seen in the newspapers.”

In a Feb. 17 speech at an Air Force Association convention in Orlando, Fla., Gen. Philip Breedlove, the service’s vice chief of staff, also said that a conventionally tipped missile, such as a modified Trident, was under consideration.

Ultimately, Scott’s second amended statement has proved correct.