WASHINGTON — The U.S. Defense Department is planning to increase investments in directed-energy systems used for missile defense over the next several budget cycles, according to the department’s top technology adviser.

Michael Griffin, undersecretary of defense for research and engineering, said Tuesday he expects to have usable directed-energy weaponry in the hands of war fighters in “no more than a few years,” but acknowledged the size of a system usable for missile defense requires greater investment.

“You need another factor of three to four to have as space control weapon, a missile defense capability — space-based, boost-phase or midcourse capability — with a large directed-energy weapon. We need to be in the megawatt class to have that,” Griffin said at an event hosted by the Center for Strategic and International Studies.

“That’s not right around the corner but that’s not utterly out of reach either. So you’re going to see in upcoming budgets for missile defense a renewed emphasis on laser scaling across several technologies because we feel we have to do that.”

Directed-energy weaponry has been a dream for decades within the department, but Pentagon planners and industry experts have become increasingly confident the use of at least small systems in the near term is realistic.

Another potential use for lower-tier systems identified by Griffin is for disrupting swarming unmanned systems, something he called a potential “transformative concern.” Using high-powered microwaves to disrupt those swarms may make sense, he predicted.

More broadly, Griffin called for a “proliferation” of sensors in low-Earth orbit to combat hypersonic threats.

“We really need to be closer to the action,” he said about the need for those systems to be in low-Earth orbit. “We need to be proliferated and reliant, so that removing a few of those satellites by the adversary doesn’t alter our capability. We need to think about space as a domain which our adversaries seek to remove from our use, and respond accordingly.”

But he underscored a point he made over the summer — that trying to catch a hypersonic weapon with a space-based interceptor simply won’t work, given the speed of hypersonic capabilities and how close to Earth they fly.

Griffin declined to comment on the status of the long-awaited Missile Defense Review, now expected no earlier than December.

Over the course of the hourlong discussion, Griffin also made an argument for why missile defense decisions should stay at the secretary of defense staffing level, guided by the Missile Defense Agency and broader strategic thinking, rather than be delegated to the armed services.

As part of a broad reorganization of the Pentagon’s acquisition structure, which also resulted in the creation of Griffin’s office, the vast majority of large acquisition programs, previously controlled by the department’s legacy acquisition office, had day-to-day oversight pushed down to the service level.

However, Griffin made it clear he thinks that would not work for the development of missile defense capabilities, flatly saying: “I don’t think it’s going to happen, and if it did, I don’t think it is going to be good.”

“Asking the Navy to prioritize an SM-3 system over another carrier, that’s maybe not a fair question. Asking the Army to prioritize THAAD over another brigade combat team, maybe that’s not a fair question,” he said. “Those are questions of the architecture of what our national defense looks like that maybe rise to the secretary or OSD level, not the responsibility of a given service.

“Today those particular systems you mentioned, THAAD and SM-3, things like that, those are prioritized at the Department of Defense level. And maybe that will just continue.”