WASHINGTON (AP) -- Senior defense officials say Pentagon chief Leon Panetta is removing 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.

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.

A senior military official says the services will develop plans for allowing women to seek the combat positions. 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 military personnel.