WASHINGTON - The Pentagon seeks to lift a decades-old policy that prohibits women from serving aboard Navy submarines, part of a gradual reconsideration of women’s roles in a military fighting two wars whose front lines can be anywhere.

At issue is the end of a policy that kept women from serving aboard the last type of ship off-limits to them. The thinking behind the previous policy was that the close quarters aboard subs would make coed service difficult to manage.

Defense Secretary Robert Gates notified Congress in a letter signed Friday that the Navy intends to repeal the ban on female sailors on submarines. Congress has 30 days to weigh in.

“He supports the Navy’s efforts to change their policy,’’ Pentagon press secretary Geoff Morrell said yesterday.

A defense official told the Associated Press that numerous physical changes to submarines would have to be made but that cadets who graduate from the Naval Academy this year could be among the first Navy women to take submarine posts.

The change was first reported by ABC News.

The official spoke on condition of anonymity because Congress has not yet had a chance to consider the recommendations.

The Navy’s plan would phase in women’s service, beginning with officers aboard larger subs, which are easier to retrofit for coed quarters. Women would never serve solo.

Because of the length of time required for training, it would be more than a year before the first women joined subs, assuming Congress raises no major objections that slow the schedule.

Last fall, Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, called for lifting the ban. Defense officials have said one reason to use women on submarines is that the number of female engineers is growing.

About 3,600 officers and 16,000 enlisted men make up the submarine force, compared with 8,000 officers and 63,000 enlisted on the surface fleet.

Women began serving aboard the Navy’s surface ships in 1993.

Since then, many of the distinctions between who is in combat and who is not have been erased.

Women are formally banned from combat posts in the Army, but routinely serve in jobs such as medics, pilots, and drivers that place them with men serving in combat jobs.

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