SAN FRANCISCO — Four female service members filed a lawsuit Tuesday challenging the Pentagon’s ban on women serving in combat, hoping the move will add pressure to drop the policy just as officials are gauging the effect that lifting the prohibition will have on morale.

The lawsuit, filed in federal court in San Francisco, is the second one this year over the 1994 rule that bars women from being assigned to ground combat units.

The legal effort comes less than a year after the ban on gays serving openly was lifted and as officials are surveying Marines about whether women would be a distraction in ground combat units.

“I’m trying to get rid of the ban with a sharp poke,” said U.S. Army Staff Sgt. Jennifer Hunt, who was among the plaintiffs in the latest lawsuit and was injured in 2007 when her Humvee ran over an improvised explosive device in Iraq.

Hunt and the other three women said the policy unfairly blocks them from promotions and other advancements open to men in combat.

Women comprise 14 percent of the 1.4 million active military personnel. The lawsuit alleges that women are barred from 238,000 positions across the Armed Forces.

At a Washington, D.C., news conference, Pentagon press secretary George Little said Defense Secretary Leon Panetta has opened about 14,500 combat positions to women.

“And he has directed the services to explore the possibility of opening additional roles for women in the military,” Little said. “His record is very strong on this issue.”

American Civil Liberties Union Ariela Migdal, who represents the four women, said Panetta’s actions weren’t enough. She called for an end to the combat ban. “These tweaks and minor changes on the margins do a disservice to all the women who serve,” she said.

“It falls short,” she said. “It is not enough.”