Washington - The nation's top military officer has called for lifting the ban on women serving aboard submarines, in a significant step toward reducing the barriers to women in combat.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said he seeks the change to broaden opportunities for women in the military. "One policy I would like to see changed is the one barring their service aboard submarines," Mullen wrote in answers to questions from Congress before his recent Senate reconfirmation hearing.

Lifting the ban would allow women for the first time to serve as officers and enlisted personnel aboard the strategic fleet of fast-attack and other submarines where sailors live and work in cramped quarters at sea for six months at a time. After combat-exclusion rules were lifted in the early 1990s, women in the Navy were allowed to serve on surface combat ships and in combat aircraft, but the ban on their employment in submarines remained.

The Navy has for years been exploring how best to bring women into its submarine force. In a statement last week, Adm. Gary Roughead, the chief of naval operations, said he is "very comfortable addressing integrating women" into the force, but added, "There are some particular issues ... we must work through."

One issue, he said, is living space. Packed with specialized gear, spare parts, and food and other supplies to operate independently for three months, a submarine is extremely cramped. On fast-attack submarines, approximately 150 personnel live in space the size of a three-bedroom house. Officers sleep in three-person staterooms, each the size of a small closet, and all 15 of them share a single shower, sink and toilet.

For female officers to live on the submarines, some three-person berths would be reserved for them and they would share the bathroom - known as a "head" - with men in a time-sharing arrangement. The submarines would have to be modified to provide adequate privacy for enlisted women and men, senior officers said.

Of greater concern, officers said, is the rate of retention for women in the Navy - about 15 percent, compared with more than 30 percent for men - and the possibility that the integration of women could lead to gaps in the relatively small submarine force. Women often leave in their late 20s to start families, although to improve retention the Navy in 2007 lengthened to one year the period that female sailors can remain ashore after childbirth.

A few years to integrate

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.

Once the ban is lifted, it would take a few years to integrate women successfully, both by training female Navy officers and enlisted personnel at all levels to move into the force and by designing a program to ensure a steady flow of women into jobs, the officials said. Integration would start with a small pilot program, said the officials, who spoke on the condition of anonymity because they were not authorized to speak on the record.

One reason the Navy seeks to integrate women on submarines is that they make up a growing percentage of college graduates, including engineers. "There is a vast pool of talent that we are neglecting in our recruiting efforts," a senior official said.

Of the 42 countries that operate submarines, Sweden, Spain, Norway, Canada and Australia allow women to serve on them, although those countries' diesel submarines go to sea for shorter periods than the nuclear submarines operated by the U.S. Navy.