Secretary of Defense Leon Panetta announced the end of a ban on women in combat roles. (The Washington Post)

The Pentagon will move “expeditiously” to integrate women into the military’s combat units, Defense Secretary Leon E. Panetta vowed Thursday, arguing that the inclusion of female troops would make the country and its fighting force stronger.

“They’re serving in a growing number of critical roles on and off the battlefield,” Panetta said shortly before signing a new policy memorandum that directed the armed services to fully integrate women. “The fact is that they have become an integral part of our ability to perform our mission.”

The change will trigger a major overhaul in how the Army and Marine Corps evaluate whether recruits and service members are fit to take on physically strenuous jobs. That process may take a couple of years to complete, officials said. It is also likely to become contentious as women try to break into the military’s most vaunted corners, such as Ranger training school and Special Operations commands.

The chairman of the Joint Chiefs of Staff, Army Gen. Martin Dempsey, who appeared alongside Panetta at a news briefing, reflected on the sweeping cultural changes since he graduated from the U.S. Military Academy at West Point in 1974, when it admitted only men.

The most eye-opening moment, he said, came in Iraq in 2003. As the commander of the 1st Armored Division, he hopped into an armored vehicle and slapped the gunner’s leg, asking the soldier to introduce himself.

The Pentagon will now allow women in the US military to fight in direct combat on the front lines, but is this decision actually centuries in the making? The Post’s Dana Priest explains what this watershed moment means for military and American culture. (The Fold/The Washington Post)

“I’m Amanda,” the gunner said, poking her head down from the turret.

“So, female turret gunner protecting a division commander,” Dempsey recalled, beaming. “And it’s from that point on that I realized something had changed and it was time to do something about it.”

In strikingly blunt terms, Dempsey said the military’s alarming rate of sexual assault and harassment cases may have been influenced by the culture created by a segregated force.

“When you have one part of the population that is designated as warriors and another that’s designated something else, I think that disparity begins to establish a psychology that in some cases led to that environment,” he said.

The new policy replaces a 1994 ban on allowing women to serve in ground combat roles. The change is the product of a decades-long debate that shifted dramatically as women served with distinction in Iraq and Afghanistan, wars with no clear front lines.

In a statement Thursday, President Obama described the move as a “historic step” and praised the service of women.

The Army and Marine Corps have been asked to present plans by May 15 outlining steps to open combat positions to women. The Marines will roll out a training exercise for 400 male and 400 female Marines next summer that will seek to start integrating women into combat units.

The Army is evaluating the way it screens soldiers for physically demanding jobs, drawing lessons from a pilot program last year in which 286 women were admitted into positions previously reserved for men.

Opposition to the plan surfaced quickly. Sen. James M. Inhofe of Oklahoma, the ranking Republican on the Senate Armed Services Committee, said in a statement that he would insist on a review and would consider introducing legislation “to stop any changes we believe to be detrimental to our fighting forces and their capabilities.”

Army officials said no one wants the inclusion of women in combat units to result in lowered standards.

“Women do not want standards changed for them,” said Gen. Robert W. Cone, who leads the Army’s training and doctrine command. “If a standard is valid, they want to be able to meet that standard.”

Women make up about 15 percent of the active-duty military. According to the Defense Department, 152 female troops have died in the Iraq and Afghanistan wars.

Pentagon officials consulted with allied nations that have integrated women into most combat jobs, including Israel, where roughly 90 percent of military jobs are open to women.

“There is nothing that women cannot achieve, and they must not be underestimated,” said retired Israeli Maj. Gen. Yitzhak Gershon, national director of the Friends of the Israel Defense Forces. “Being a small country under constant threats, we cannot afford to discriminate,” Gershon said.

Joy Naughton was disappointed when she learned that her gender made her ineligible to join a Navy support unit that delivers and picks up Navy SEALs from dangerous missions. The 24-year-old opted instead to join the Navy’s aviation rescue swimmer program, which trains sailors to jump out of a helicopter to save a downed pilot.

Speaking over the phone while riding a van with 16 loud prospective Navy SEALs, Naughton said she was thrilled by the new policy.

“I think it’s awesome,” she said, “but I still think there needs to be a hard selective process. They can’t let just any woman into combat. It takes a special kind of individual.”