More

• Gen. Dempsey's Letter to Defense Secretary Panetta

The change is an acknowledgment that women on modern battlefields already are in the fight—152 women have died in Iraq and Afghanistan—and that military rules need to be updated to reflect realities of the current-day war zones. At the same time, the shift establishes a process that could take years to complete.

The new policy should allow women to serve alongside infantry troops as battlefield medics, special-operations pilots and in other dangerous roles, officials said. But officials are divided about whether women will ultimately serve as infantry troops or in elite special-operations units. Some military officials, citing the difficulty of completing infantry training courses, believe that most women would be unable to meet the physical requirements.

Army Staff Sgt. Jennifer Hunt, who was injured in 2007 by a roadside bomb in Iraq, said in an interview Wednesday that the current ban on women in combat is "a legal fiction." She said women have long faced the same front-line dangers from militants and improvised explosive devises as men.

"Right before the IED went off, it didn't ask me how many push-ups or sit-ups I could do," said Ms. Hunt, one of the women who filed a lawsuit last year to challenge the ban. "Right now the women who are serving are being engaged in combat, so their physical restrictions aren't a barrier."

A female Marine and members of the Navy Hospital Corpsman walked at Forward Operating Base Jackson in Sangin, Helmand province, Afghanistan, on June 7, 2012.

U.S. military services over the next two years will examine all 230,000 positions women currently are excluded from. They also will be required to establish gender-neutral requirements for admission and decide whether women can serve alongside men. "The goal is to make all roles available so long as we can meet the standards of the war fighter," said a defense official.

The policy shift follows a study by the Joint Chiefs of Staff that determined the military could become much more aggressive at allowing women into excluded roles. "The time has come to rescind the direct combat exclusion rule for women and eliminate all unnecessary gender-based barriers to service," Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, wrote in a Jan. 9 memo to Mr. Panetta.

"Does that mean that women are going to be full-up Navy SEALs? Probably not," said Maren Leed, an analyst at the Center for Strategic and International Studies who served until last year as a senior adviser to the U.S. Army chief of staff. "It probably means there will be sub-specialties within the SEALs for which they are eligible."

Women regularly have found themselves in battle in Iraq and Afghanistan, whether in supply convoys or in military police units.

A number of other countries allow women in some combat roles, including Canada, Australia and New Zealand.

Last February, Mr. Panetta ordered U.S. military service chiefs to find ways to expand the role of women. Under that decision, approximately 14,300 new positions were opened to women.

The shift was hailed by both Democrats and Republicans on Capitol Hill. Sen. Kelly Ayotte (R, N.H.) said she was pleased by the announcement and Sen. Jack Reed (D, R.I.) said that on the current battlefield "all who serve are in combat."

Rep. Tammy Duckworth (D., Ill.), a former Army pilot who lost both her legs in Iraq when her helicopter was hit by a rocket-propelled grenade, said the decision will allow the "best man or woman on the front line."

Added Rep. Tulsi Gabbard (D., Hawaii), an Army National Guard member who deployed to Iraq as a medical specialist and was elected to Congress in November: "Female service members have contributed on the battlefield as far back as the Civil War, when some disguised themselves as men just to have the opportunity to serve their nation." She said the decision "is an overdue, yet welcome change, which I strongly support."

But some lawmakers criticized the Pentagon's move and questioned whether physical requirements would permit women to enter combat duty in large numbers.

"The focus of our military needs to be maximizing combat effectiveness," said Rep. Duncan Hunter (R., Calif.). "The question here is whether this change will actually make our military better at operating in combat and killing the enemy, since that will be their job, too."

Last year, two women tried to complete the Marine Corps's 13-week infantry officer's training course at Quantico, Va. One did well, but eventually had to drop out because of stress fractures. Marine Corps officials plan to try again this year.

Under the new rules, the services must establish the gender-neutral standards for all military specialties by September 2015. In his memo, Gen. Dempsey also ordered U.S. Special Operations Command, along with the military services, to examine a "responsible way to assign women to currently closed" military specialties.

Beginning later this year, under Gen. Dempsey's memo, the service chiefs must provide regular progress reports on their efforts to expand the positions women may hold. A defense official said that after Thursday, any restriction sought by the services on women's service roles must be approved by the secretary of defense.

Twenty years ago, Congress lifted the ban on women flying in attack aircraft, and now the Army, Marines, Navy and Air Force all have women pilots—although women don't serve as special-operations pilots.

Female officers now serve on large submarines, and the Navy has plans to add female enlisted personnel on those vessels. The Navy also will allow women to serve on smaller classes of submarines. As the military considers sweeping changes for women, a senior Air Force leader told a House panel examining a sexual-abuse scandal at a Texas base on Wednesday that his branch of the military needs to improve its culture to root out problems, such as binge drinking and vulgar images, that can be conducive to sexual harassment.

Obscene images, songs and stories "will not be accepted as part of our culture," Gen. Mark Welsh III, the Air Force chief of staff, told the House Armed Services Committee, which is investigating allegations of widespread sexual misconduct at the Air Force's facility for basic military training in San Antonio, where enlisted members begin their service.