The Army and Marine Corps' top uniformed leaders both backed making women register for the draft as all combat roles are opened to them in coming months, a sweeping social change that could complicate the military's gender integration plans.

Both services, along with the Navy, have begun work to open all military jobs to any service member after a decision by Defense Secretary Ash Carter in December to lift all gender-based restrictions on combat and infantry roles.

On Tuesday, Army Chief of Staff Gen. Mark Milley and Marine Corps Commandant Gen. Robert Neller told senators during a Capitol Hill hearing that full integration of those jobs will likely take a few years, to overcome logistical and cultural issues.

One of those complications will be how to handle the Selective Service System, which requires all men ages 18 to 26 to register for possible involuntary military service.

Women have always been exempt, and past legal challenges have pointed to the battlefield restrictions placed on them. With that reasoning moot, lawmakers will need to determine what becomes of the system.

Navy Secretary Ray Mabus Jr. said there needs to be "a national debate" over what the changes mean, balancing social concerns over the idea of drafting women with the reality of national security and military readiness.

But the uniform leaders were more blunt in their assessment.

"It's my personal view in light of integration that every American physically qualified should register for the draft," Neller said. Milley echoed those remarks, saying "all eligible men and women" should be required to register.

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The comments drew support from some Democratic lawmakers — "I agree with you," said Sen. Claire McCaskill, D-Mo. — but concerned looks from Republicans on the Senate Armed Services Committee, who spent most of the hearing criticizing how abruptly the decision to drop gender restrictions was made.

Several pressed military leaders over whether job standards would be lowered to allow women into combat roles, a charge officials repeatedly refuted.

Milley and Neller said no quotas for positions have been set. Mabus said that watering down physical standards is "unacceptable under the law, and unacceptable to me and every other senior leader in the Pentagon, because it would endanger not only the safety of Marines, but also the safety of our nation."

But committee chairman Sen. John McCain, R-Ariz., said military officials still have not provided enough study or implementation plans to justify the rapid changes laid out by military leaders.

"I am concerned that the department has gone about things backward," he said. "This consequential decision was made and mandated before the military services could study its implications, and before any implementation plans were devised to address the serious challenges raised in studies."

Sen. Joni Ernst, R-Iowa — the only female veteran on the Senate committee — said she fully supported the changes "as long as standards are not lowered" to boost the number of women in combat jobs or force them to meet quotas.

"We need to ensure we don't set up men or women for failure," she said. "It's clear we need to ensure that we're taking into account the impact this could have on women's health.

Marine Corps officials had requested to leave some of their infantry and combat jobs closed to women, citing a service study showing concerns about unit effectiveness. Carter denied those requests.

For many advocates, the controversy over women in combat jobs is an outdated debate.

Army leaders noted at Tuesday's hearing that more than 9,000 women have already earned the Combat Action Badge for actions in the wars in Iraq and Afghanistan. More than 1,000 women have been killed or wounded in that fighting.

Leo Shane III covers Congress, Veterans Affairs and the White House for Military Times. He can be reached at lshane@militarytimes.com.