Multiple officials confirm to CNN that Defense Secretary Leon Panetta will make the announcement tomorrow and notify Congress of the planned change in policy.
"We will eliminate the policy of 'no women in units that are tasked with direct combat,'" a senior defense official says.
But the officials caution that "not every position will open all at once on Thursday." Once the policy is changed, the Department of Defense will enter what is being called an "assessment phase," in which each branch of service will examine all of its jobs and units not currently integrated and then produce a timetable in which it can integrate them.
The Army and Marine Corps, especially, will be examining physical standards and gender-neutral accommodations within combat units. Every 90 days, the service chiefs will have to report back on their progress.
The move will be one of the last significant policy decisions made by Panetta, who is expected to leave in mid-February. It is not clear where former Sen. Chuck Hagel, the nominated replacement, stands, but officials say he has been apprised of Panetta's coming announcement.
"It will take awhile to work out the mechanics in some cases. We expect some jobs to open quickly, by the end of this year. Others, like Special Operations Forces and Infantry, may take longer," a senior defense official explains. Panetta is setting the goal of January 2016 for all assessments to be complete and women integrated as much as possible.
The Pentagon has left itself some wiggle room, however, which may ultimately lead to some jobs being designated as "closed" to women. A senior Defense official says if, after the assessment, a branch finds that "a specific job or unit should not be open, they can go back to the secretary and ask for an exemption to the policy, to designate the job or unit as closed."
The official says the goal remains to open as many as possible. "We should open all specialties to the maximum extent possible to women. We know they can do it."
The Pentagon must notify Congress of each job or unit as it is sent up to the secretary to be "opened" to women. And then the Defense Department must wait 30 days while Congress is in session before implementing the change.
It is a marked difference from the way the military ended the exclusion of gays serving openly, or "don't ask don't tell." In that case, there were no stipulations attached to openly gay service members. There was no staggered approach that integrated openly gay troops into units. It was instead done all at once, across the board.
A senior Defense official explained the Pentagon's reasoning behind the different approach: "You're talking about personal choice of behavior vs. physical capability. And they were already in the units. If you take a unit that's never had women before, that's quite a culture change."
Another senior Defense official says the goal is "to provide a level, gender-neutral playing field."
The American Civil Liberties Union recently filed a federal lawsuit against the Department of Defense, charging that combat exclusion is unfair and outdated, harms America's safety and prevents women from getting training and recognition for their work. The plaintiffs, who include women awarded Purple Hearts, say the exclusion places them at a disadvantage for promotion.
Earlier this month, the Army opened the 160th Special Operations Aviation Regiment to women, and it has begun recruiting female pilots and crew chiefs. The Navy has put its first female officers on submarines in the past year, and certain female ground troops have been "attached" to combat units in Iraq and Afghanistan. More than 800 women were wounded in those wars, and at least 130 have died.