WASHINGTON — Women in the military must have the same opportunities as men to take on grueling and dangerous combat jobs, whether loading 50-pound artillery shells or joining commando raids to take out terrorists, defense leaders declared Thursday as they ordered a quarter-million positions open to service members regardless of gender.

As Defense Secretary Leon Panetta and Gen. Martin Dempsey, chairman of the Joint Chiefs, signed an order wiping away generations of limits on women fighting for their country, the military services said they would begin a sweeping review of the physical requirements. At the same time they acknowledged that women have been fighting and dying in Iraq and Afghanistan for more than a decade.

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

The leaders said no physical standards will be lowered just to send more women closer to the battlefront. “I fundamentally believe that our military is more effective when success is based solely on ability and qualifications and on performance,” Panetta said at a Pentagon news conference. “Not everyone is going to be able to be a combat soldier. But everyone is entitled to a chance.”

It won’t happen quickly or easily. But in the end, he said, the U.S. military and America will be stronger for it.

Dempsey did not rule out women serving even as members of elite special operations forces, including the Army’s Delta Force and the Navy’s SEALs, whose members killed 9/11 mastermind Osama bin Laden.

Dempsey said that because of the particularly punishing physical standards and training required for those teams, it might be years before they include women.

But he added: “I think we all believe that there will be women who can meet those standards.”

Recent surveys and experiences suggest the transition may not always be easy. 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 clamoring from women for the more intense, dangerous and difficult jobs.

Representatives of the military services said they will look at each job and military specialty that is currently closed to women and examine the requirements that troops must meet. In some cases — because of equipment upgrades, new technology and automation — the requirements may change, but in no case will they lower the standards in order to allow women to qualify.

Troops asked about the change said they just want comrades who can do the job. “This gives us more people to work with,” said Sgt. Jeremy Grayson, assigned to field infantry at Fort Bliss, Texas. “But they would have to be able to do the physical stuff that men do. Like in some jobs in infantry you’re out there for a long time, or in artillery there is heavy work. And they have to be able to pull their own weight.”