WASHINGTON — Defense Secretary Leon E. Panetta is planning to lift the ban on women serving in ground combat units, removing one of the military’s last major gender barriers and opening up more than 230,000 combat jobs to females, senior Defense officials said.

The historic decision, which Panetta is expected to announce Thursday, means women serving in the Army and Marines may soon be assigned for the first time to combat roles in infantry, armor and field artillery battalions, companies, platoons and squads.

Although the move raises the likelihood that female troops will suffer far higher casualties in future wars, women’s veterans groups applauded the move as long overdue and in line with other sweeping changes in American culture.

“There is going to be some foot-dragging, of course,” said Tara Jones, a Navy veteran and president of the National Military Women Veterans Assn. of America, based in San Diego. “People don’t like change, and our military is a male-oriented society.”

Retired Navy Rear Adm. Veronica “Ronne” Froman, the first woman to command Navy Region Southwest in San Diego, said she was overjoyed. “This has been what we’ve been working for for a long time,” she said. “Women were the last minority in the Navy.”

But Elaine Donnelly, president of the Center for Military Readiness, a conservative advocacy group based in Livonia, Mich., criticized the decision, arguing that women are less capable than men in warfare.

“Women do not have an equal opportunity to survive or help fellow soldiers survive in direct ground combat,” Donnelly said.

The Army and the Marines have long resisted putting women in combat units, arguing that they lacked the strength and agility to fight and survive in the harshest conditions. But officials said Gen. Martin Dempsey, chairman of the Joint Chiefs, and the other service chiefs supported the move to end the ban.

Panetta will direct the chiefs of the Army, Air Force, Navy and Marines to develop plans for integrating women into combat units by 2016. He will order each branch to provide initial blueprints by this spring, and the services are expected to start implementing the policy fairly quickly.

Each service may seek to keep some positions closed to women, but the goal will be to keep those exceptions to a minimum, senior Defense officials said.

The services will be allowed to set physical fitness requirements and other standards for combat jobs, but the standards will be gender-neutral, said the officials, who spoke on condition of anonymity because Panetta had not yet made the announcement.

“The presumption now is that all jobs will be open, instead of the old rule that presumed females would be kept out of ground combat,” one official said.

Panetta’s decision specifically lifts a 1994 Pentagon rule that bars women from serving in jobs that makes them likely to engage in direct ground fighting.

Congress will have a month to review the decision before it goes into effect, and in theory could block lifting the rule, though that is unlikely, officials said.

The immediate reaction in Congress was mixed. Sen. John McCain (R-Ariz.), a Vietnam combat veteran who sits on the Senate Armed Services Committee, tweeted: “I respect and support” Panetta’s decision “to lift the ban on women serving in combat.”

But Rep. Duncan Hunter (R-Alpine), a Marine veteran of Iraq and Afghanistan, said Panetta needed to explain “how this decision … increases combat effectiveness rather than being a move done for political purposes — which is what this looks like.”

The Air Force and the Navy are well ahead of the other services in integrating women into their forces, largely because neither service is heavily involved in ground combat. Women pilots have flown in combat since 1993, for instance.

But even the Air Force bars females from serving in certain ground assignments, including combat air controllers, who are assigned to ground units to call in air strikes, or so-called para-rescue specialists, who slip behind enemy lines to help find downed pilots.

“The American public is ready to accept a greater number of female casualties in wartime,” said Lory Manning, a retired U.S. Navy captain. “Everyone expected a hue and cry when women started getting killed in combat, and it hasn’t happened.”

In all, 241,000 women are on active duty in the armed forces, out of 1.6 million Americans in uniform. Over the last decade, 61 female service members were killed in action in Iraq and 23 have died in Afghanistan.

Opposition to women in combat has eased in the last decade as the number of women serving in the armed forces has grown, and the unconventional wars in Iraq and Afghanistan, with their lack of front lines and unconventional fighting, have sometimes put women in as much danger as men firing weapons.

Due to the demand for troops, women often found themselves working on the front lines as drivers, medics, mechanics and other roles when commanders attached their units to combat battalions.

Panetta, who plans to step down as Defense secretary in the coming weeks, has made easing restrictions on women in combat one of his major priorities.

Last year, he allowed women for the first time to serve in combat support jobs in Army and Marine battalions. The move opened up 14,000 new jobs to women, mostly in the Army and Marines. But putting a woman at company level or below required special permission, and combat assignments such as infantryman were still prohibited.

Susan Farrell of San Diego, who served on a Department of Defense advisory committee that recommended opening more jobs to women, lauded the decision as “a chance for women to sink or swim on their own merits. That’s all women have ever asked for: a chance to be as patriotic, as giving of themselves, as the men are.”

Nancy Duff Campbell, co-president of the nonprofit National Women’s Law Center, based in Washington, said Panetta’s decision eliminated “the last vestige of government-sanctioned sex discrimination in the United States.”

david.cloud@latimes.com

tony.perry@latimes.com

Shashank Bengali in Washington and David Zucchino in Raleigh, N.C., contributed to this report.