WASHINGTON -- A measure to let women fight on the front lines is part of the massive defense bill proposed Thursday in the Senate.

The National Defense Authorization Act, unveiled by Sens. Carl Levin (D-Mich.) and John McCain (R-Ariz.), includes a proposal offered last week by Sen. Kirsten Gillibrand (D-N.Y.) that would order the military to come up with a plan to send women into battle.

The Defense Department last week began relaxing its ground combat exclusion policy for women, opening some jobs closer to traditional battlefields. The Gillibrand provision would require commanders to make plans to remove the final barriers for woman warriors.

Women constitute about 15 percent of the armed forces, and 144 have died in action in Iraq and Afghanistan. Nearly 900 have been wounded there. Supporters of opening all war zones to women say such a change would also remove obstacles to women's advancement in the military, where battle experience is a key to promotion.

"Women are already fighting and dying for our country shoulder-to-shoulder with their brothers in uniform on the front lines, but without the formal recognition that is essential for them to advance and obtain the benefits they have earned," said Gillibrand in a statement. "Just like it was wrong to discriminate against service members because of whom they love, it is also wrong to deny combat roles to qualified women solely because of their gender."

Gillibrand originally wanted to give the military a year to detail a plan to end the battle barrier, but settled for an open-ended deadline in order to get the process moving.

Although the House version of the defense legislation lacks the combat provision for women, a separate bill is pending in the lower chamber, and the measure could be added later when the House and Senate mesh their two defense bills, likely in the fall.

"I'm glad to see the inclusion of this legislation in the Senate's NDAA," said Rep. Loretta Sanchez (D-Calif.), sponsor of the House bill. "By requiring this report, the Senate Armed Services Committee is continuing to build the momentum that will one day make repeal of the combat exclusion policy possible."

Michael McAuliff covers politics and Congress for The Huffington Post. Talk to him on Facebook.

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