Defense Secretary Leon Panetta will remove the military's ban on women serving in combat, opening hundreds of thousands of front-line positions and potentially elite commando jobs after more than a decade at war, a senior defense official confirmed Wednesday.

The groundbreaking move recommended by the Joint Chiefs of Staff overturns a 1994 rule prohibiting women from being assigned to smaller ground combat units. Panetta's decision gives the military services until January 2016 to seek special exceptions if they believe any positions must remain closed to women.

“This policy change will initiate a process whereby the services will develop plans to implement this decision, which was made by the secretary of defense upon the recommendation of the Joint Chiefs of Staff,” a senior defense official said.

Some jobs may open as soon as this year. Assessments for others, such as special operations forces, including Navy SEALs and the Army's Delta Force, may take longer.

The official said the military chiefs must report back to Panetta with their initial implementation plans by May 15. The announcement on Panetta's decision is not expected until Thursday, so the official spoke on condition of anonymity.

Panetta's move expands the Pentagon's action nearly a year ago to open about 14,500 combat positions to women, nearly all of them in the Army. This decision could open more than 230,000 jobs, many in Army and Marine infantry units, to women.

In recent years, the necessities of war propelled women into jobs as medics, military police and intelligence officers that were sometimes attached -- but not formally assigned -- to units on the front lines.

Women comprise 14 percent of the 1.4 million active-duty military personnel.

The Washington Times obtained a copy of the memorandum entitled “Women in the Service Implementation Plan” by Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff.

“The time has come to rescind the direct combat exclusion rule for women and to eliminate all unnecessary gender-based barriers to service,” Dempsey wrote in the memo, dated Jan. 9.

Dempsey explained that the vote to lift the ban was unanimous among the Joint Chiefs of Staff.

“The Joint Chiefs of Staff unanimously join me in proposing that we move forward with the full intent to integrate women into occupational fields to the maximum extent possible,” Dempsey wrote, according to the Washington Times report. “To implement these initiatives successfully and without sacrificing our warfighting capability or the trust of the American people, we need time to get it right.”

Last year, the American Civil Liberties Union filed a federal lawsuit, naming Panetta as the defendant, on behalf of four military women challenging the combat exclusion as unconstitutional.

“The combat exclusion policy is based on outdated stereotypes of women and ignores the realities of the modern military and combat conditions,” the lawsuit said.

The ACLU responded to the announcement Wednesday with cautious optimism.

“We are thrilled to hear Secretary Panetta’s announcement today recognizing that qualified women will have the same chance to distinguish themselves in combat as their brothers-in-arms, which they actually already have been doing with valor and distinction,” said Ariela Migdal, an attorney for the ACLU Women’s Rights Project, in a statement on Wednesday.

Migdal said in the statement that she hoped the new policy would be “implemented fairly and quickly so that servicewomen can receive the same recognition for their service as their male counterparts.”

Sen. Patty Murray, D-Wash., said the move is an historic step for equality and recognizing the role women have already been playing in defending the country. In Iraq and Afghanistan, there have been no front lines. Women -- whether acting as drivers or interpreters -- have encountered the same danger and hostile fire as their male counterparts, Murray said.

“From the streets of Iraqi cities to rural villages in Afghanistan, time and again women have proven capable of serving honorably and bravely,” she said.

Iraq War veteran U.S. Rep. Tulsi Gabbard, D-Hawaii, called the Pentagon decision “long overdue” and pointed out in a statement that American women have been serving "on the battlefield as far back as the Civil War, when some disguised themselves as men just to have the opportunity to serve their nation.”

Gabbard is one of the first female combat vets to serve in Congress. She deployed to Iraq in 2004 as an enlisted soldier with a medical company of the 29th Brigade Combat Team. A few years later, as an officer, she was again deployed to the Middle East, including Kuwait.

“I look forward to hearing the details of how this [change] will be executed, and will support full and equal access for our highly capable female servicemembers to serve our country in all roles,” she said in her statement.

Civil liberties organizations were quick to applaud the announcement, with Nancy Duff Campbell, co-president of the National Women’s Law Center, calling it a “historic day” marking the end of “the last vestige of government-sanctioned sex discrimination in the United States."

“Now if the best person for the job is a woman, she will no longer be barred from that job simply because of her gender,” Campbell said.

-- Michael Hoffman and the Associated Press contributed to this report.