"Every citizen who can meet the qualifications of service should have the opportunity to protect the nation," Panetta said during the press conference announcement.
But the officials caution that "not every position will open all at once on Thursday."
The Department of Defense will enter into an 'assessment phase' following Thursday's announcement, in which it will examine the non-integrated units to determine how long the integration will take.
"It will take awhile to work out the mechanics in some cases,” a senior defense official explains. "We expect some jobs to open quickly, by the end of this year. Others, like Special Operations Forces and Infantry, may take longer."
Panetta, who will depart his Cabinet post sometime in the coming weeks or months, is reportedly setting a goal of January 2016 for the completion of the assessments and integration.
The officials said the Pentagon may leave some positions 'closed' to women, allowing each branch of the military to determine positions for which they will ask for exemptions.
The ban on women serving in combat roles was put on the books in 1994, when the Pentagon established its 'ground combat exclusion policy.
The policy states:
"Service members are eligible to be assigned to all positions for which they are qualified, except that women shall be excluded from assignment to units below the brigade level whose primary mission is to engage in direct combat on the ground."
Notable deaths of 2014 [PHOTOS]
Soviets call Reagan joke 'dangerous' [ARCHIVE]