But Elaine Donnelly, president of the Center for Military Readiness, a nonprofit group that studies military personnel policies and opposes women in combat, said the change was “irresponsible.”

“For the same reason you don’t see women in the NFL, you shouldn’t see women in combat units,” she said. “Women are not the equal of men.”

One argument against the ban was the idea that while women face death or injury in modern wars, the ban also denied many military career fields, necessary training and hurt their chances at promotions.

The ACLU’s Migdal also said that commanders often found their hands tied in trying to figure out how to get needed skills into dangerous areas and yet obey the ban. In October, for instance, an attack by a Taliban suicide bomber in Khost, Afghanistan, killed three American service members, including Staff Sgt. Donna Johnson of Raeford, N.C.

Still, Michael O’Hanlon, a military expert with the Washington-based Brookings Institution, said putting women into “frontline combat positions is a very delicate matter.” While details of how to make this decision work haven’t yet been worked out, he said, “The right process seemed more incremental, perhaps starting with the special forces.”

However the policy is carried out, Sen. Patty Murray, D-Wash., chairwoman of the Senate Veterans’ Affairs Committee, said that lifting the ban is “an historic step for equality. . . . From the streets of Iraqi cities to rural villages in Afghanistan . . . thousands of women already spent their days in combat situations serving side by side with their fellow male service members.”

Donald Bradley of The Kansas City Star contributed.