WASHINGTON -- Defence Secretary Leon Panetta, in lifting a ban on women serving in combat, said women have become integral to the U.S. military's success and have shown they are willing to fight and die alongside their male counterparts.

"The time has come for our policies to recognize that reality," Panetta said Thursday at a Pentagon news conference with Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff.

Panetta said that not all women will be able to meet the qualifications to be a combat soldier.

"But everyone is entitled to a chance," he said.

He said the qualifications will not be lowered, and with women playing a broader role, the military will be strengthened.

President Barack Obama supports the Pentagon's decision and believes the country should continue to remove "unnecessary gender-based barriers to service, " White House spokesman Jay Carney told reporters.

More than 150 women have been killed in wars in Iraq and Afghanistan while serving in support roles. The decision to lift the ban on them serving in combat presents a daunting challenge to top military leaders who will now have to decide which jobs, if any, should be open only to men.

Women comprise about 14 per cent of the 1.4 million active military personnel. More than 280,000 women have been sent to Iraq, Afghanistan or to jobs in neighbouring nations in support of the wars. Of the more than 6,600 U.S. service members who have been killed, 152 have been women.

Panetta said that his visits to Afghanistan and Iraq to see U.S. forces in action demonstrated to him that women should have a chance to perform combat duties if they wish, and if they can meet the qualifications.

"Our military is more capable, and our force is more powerful, when we use all of the great diverse strengths of the American people," Panetta said earlier Thursday at a Pentagon ceremony in remembrance of slain civil rights leader Martin Luther King Jr.

Panetta is expected to step down as Pentagon chief sometime in February. Republican former Sen. Chuck Hagel has been nominated as his successor, and his Senate confirmation hearing is scheduled for Jan. 31.

"Every person in today's military has made a solemn commitment to fight, and if necessary to die, for our nation's defence," he said. "We owe it to them to allow them to pursue every avenue of military service for which they are fully prepared and qualified. Their career success and their specific opportunities should be based solely on their ability to successfully carry out an assigned mission. Everyone deserves that chance."

Panetta planned to announce at a Pentagon news conference that more than 230,000 battlefront posts -- many in Army and Marine infantry units and in potentially elite commando jobs -- are now open to women. It will be up to the military service chiefs to recommend and defend whether women should be excluded from any of those more demanding and deadly positions, such as Navy commandos or the Army's Delta Force.

Alma Felix, a 27-year-old former Army specialist, said she hopes the decision will lead society to recognize that women, too, can be courageous warriors.

"We disappear into the background," said Felix, who served in Iraq. "You always hear we're losing our sons out there. And although women have fallen out there, you really don't see very much of it."

"We are the support. Those are the positions we fill and that's a big deal -- we often run the show -- but people don't see that," she added. "Maybe it will put more females forward and give people a sense there are women out there fighting for our country.

The historic change, which was recommended by the Joint Chiefs of Staff, overturns a 1994 rule prohibiting women from being assigned to smaller ground combat units.

The change won't take place overnight: Service chiefs will have to develop plans for allowing women to seek the combat positions, a senior military official said. Some jobs may open as soon as this year, while assessments for others, such as special operations forces, may take longer. The services will have until January 2016 to make a case to that some positions should remain closed to women.

Officials briefed The Associated Press on the changes Wednesday on condition of anonymity so they could speak ahead of the official announcement.

There long has been opposition to putting women in combat, based on questions of whether they have the necessary strength and stamina for certain jobs, or whether their presence might hurt unit cohesion.

But as news of Panetta's expected order got out, many members of Congress, including the Senate Armed Services Committee chairman, Sen. Carl Levin, a Democrat, announced their support.

"It reflects the reality of 21st century military operations," Levin said.

Objections were few. Jerry Boykin, executive vice-president of the Family Research Council, called the move "another social experiment" that will place unnecessary burdens on military commanders.

"While their focus must remain on winning the battles and protecting their troops, they will now have the distraction of having to provide some separation of the genders during fast-moving and deadly situations," said Boykin, a retired Army lieutenant general. He noted that small units often are in sustained combat for extended periods of time under primal living conditions with no privacy.

Panetta's move comes in his final weeks as Pentagon chief and just days after President Barack Obama's inaugural speech in which he spoke passionately about equal rights for all. The new order expands the department's action of nearly a year ago to open about 14,500 combat positions to women, nearly all of them in the Army.

In addition to questions of strength and performance, there also have been suggestions that the American public would not tolerate large numbers of women being killed in war.

Under the 1994 Pentagon policy, women were prohibited from being assigned to ground combat units below the brigade level. A brigade is roughly 3,500 troops split into several battalions of about 800 soldiers each. Historically, brigades were based farther from the front lines, and they often included top command and support staff.

The necessities of combat in Iraq and Afghanistan, however, propelled women into jobs as medics, military police and intelligence officers that were sometimes attached -- but not formally assigned -- to battalions. So while a woman couldn't be assigned as an infantryman in a battalion going out on patrol, she could fly the helicopter supporting the unit, or move in to provide medical aid if troops were injured.

And these conflicts, where battlefield lines are blurred and insurgents can lurk around every corner, have made it almost impossible to keep women clear of combat.

Still, as recent surveys and experiences have shown, it will not be an easy transition. When the Marine Corps sought women to go through its tough infantry course last year, two volunteered, and both failed to complete the course. And there may not be a wide clamouring from women for the more intense, dangerous and difficult jobs, including some infantry and commando positions.