WASHINGTON — Outgoing Defense Secretary Leon Panetta plans to announce on Thursday a lifting of the ban on women in combat roles on, a watershed change that removes the remaining barrier to a fully inclusive military, defense officials said.
Panetta made the decision ‘‘upon the recommendation of the Joint Chiefs of Staff,’’ a senior defense official said Wednesday, an assertion that stunned female veteran activists who said they assumed that the brass was still uneasy about opening the most physically arduous positions to women. Officials said the decision was influenced by women’s valor in Iraq and Afghanistan.
The Army and the Marines, which make up the bulk of the ground combat force, will present plans to open most jobs to women by May 15.
The Army, by far the largest fighting force, currently excludes women from nearly 25 percent of active-duty roles. A senior defense official said the Pentagon expects to open ‘‘many positions’’ to women this year; senior commanders will have until January 2016 to ask for exceptions.
‘‘The onus is going to be on them to justify why a woman can’t serve in a particular role,’’ said the official, who spoke on the condition of anonymity to discuss the plan before the official announcement.
The decision comes after a decade of counterinsurgency missions in Iraq and Afghanistan, where women demonstrated heroism on battlefields with no front lines. It dovetails with another seismic policy change in the military that has been implemented relatively smoothly: the repeal of the ban on openly gay service members.
Lawmakers and female veterans applauded Wednesday’s news, saying the ban on women in combat roles is obsolete.
‘‘This is monumental,’’ said Anu Bhagwati, a former Marine captain and executive director of the Service Women’s Action Network, which has advocated for the full inclusion of women. ‘‘Every time equality is recognized and meritocracy is enforced, it helps everyone, and it will help professionalize the force.’’
Critics of opening combat positions to women have argued for years that integration during deployments could create a distracting, sexually charged atmosphere in the force and that women are unable to perform some of the more physically demanding jobs.
Advocates and experts say women are unlikely to flock to those positions, such as roles in light infantry and tank units and Special Forces — although some may. More substantively, they say, lifting the ban will go a long way toward changing the culture of a male-dominated institution in which women have long complained about discrimination and a high incidence of sexual assault.
Advocates have long pressed the Pentagon to create a more inclusive force, yielding incremental changes. The American Civil Liberties Union sued the Pentagon over its policy, calling it discriminatory.
Last year, military officials opened numerous job categories to women after a study concluded that the Defense Department was ready for greater inclusion in combat units. That made it easier for women to be assigned, for example, to combat brigades as radio operators. It also gave commanders a sense of how a broader integration process could work, said an Army general who played a key role in last year’s effort to open new positions for women.
‘‘The average professional will say, ‘I’ve served with women at all levels, and based on my experience, women have done a phenomenal job,’ ‘‘ said the officer, who spoke on the condition of anonymity because the change had not been formally announced.
The debate over the supposed pitfalls of women and men sharing close quarters has been rendered moot by the recent wars, he said, adding: ‘‘If you were having this debate in peacetime, it might be more emotional.’’
The fact that women have excelled in de facto front-line roles in Iraq and Afghanistan has proved such concerns unwarranted, Senator Carl Levin, Democrat of Michigan and the head of the Senate Armed Services Committee, said in an interview.
‘‘The reality is that so many women have been, in effect, in combat or quasi-combat,’’ he said. ‘‘This is catching up with reality.’’
Senator John McCain, Republican of Arizona and a member of the Armed Services Committee, said he supports the decision but alluded to some thorny implementation issues to be addressed.
‘‘It is critical that we maintain the same high standards that have made the American military the most feared and admired fighting force in the world — particularly the rigorous physical standards for our elite special forces units,’’ he said in a statement.
The senior defense official said the Pentagon expects to have gender-neutral standards for combat jobs.
Overall, women make up about 14 percent of the active-duty military. According to the Defense Department, 152 female troops have been killed in the Iraq and Afghan wars.