The Pentagon will maintain bans on women serving in most ground combat units, defense officials said Thursday, despite pressure from lawmakers and female veterans who called the restrictions outdated after a decade of war.

After taking more than a year to review its policies on orders from Congress, the Defense Department announced that it would open about 14,000 combat-related positions to female troops, including tank mechanics and intelligence officers on the front lines.

But the Pentagon said it would keep 238,000 other positions — about one-fifth of the regular active-duty military — off-limits to women, pending further reviews. Virtually all of those jobs are in the Army and Marine Corps.

Pentagon officials said that they were committed to lifting barriers to women but that it was difficult to make sweeping changes on the battlefield during a time of war.

“Sometimes this takes longer than you’d like,” said Virginia S. Penrod, the deputy assistant secretary of defense for military personnel policy. “It may appear too slow to some, but I see this as a great step forward.”

In the 1970s, Penrod recalled, she was one of the first women allowed to serve at Minot Air Force Base in North Dakota. Female troops had previously been banned there because it was “too cold,” she said, adding that the military has come a long way since then.

Advocates for women in the military, however, accused the Pentagon of dragging its feet and only belatedly recognizing the critical role that female troops have played in the wars in Afghanistan and Iraq. They said many of the job openings announced by the Pentagon merely codify the reality on the battlefield, where commanders have stretched rules for years to allow women to bear arms and support ground combat units.

Since 2001, about 280,000 women have deployed to Iraq and Afghanistan, according to Defense Department statistics; 144 have been killed, and 865 have been wounded.

The biggest previous advance for women in uniform came in 1994, when the Clinton administration removed restrictions on more than a quarter-million troop slots. Since then, however, the Pentagon has kept in place a prohibition on women serving in units whose primary mission is “direct” ground combat, such as artillery, infantry and tank units.

“Since then, it’s been drip, drip, drip,” said Nancy Duff Campbell, co-president of the National Women’s Law Center, expressing frustration with what she called incremental changes. “This is the pattern that they have been following for years.”

Pressure for more changes has been building in Congress, particularly among female lawmakers.

In March, a congressional commission recommended that the ban on women serving in ground combat units be overturned as part of a broader effort to increase diversity in the armed forces, particularly in the officer ranks.

Congress separately ordered the Defense Department to review the ban and submit recommendations. That review was due last April, but the Pentagon took an extra 10 months to complete it.

Part of the reason for the delay was that the military was in the midst of another big social change: the repeal of the “don’t ask, don’t tell” policy, which prevented gay troops from serving openly. The ban was lifted in September.

Women in the Army and Marine Corps face the most job restrictions, with each prohibiting them from serving in about a third of its positions.

In contrast, the Air Force excludes women from 1 percent of its positions, and the Navy places about 12 percent of its jobs off-limits, many of them aboard submarines. The Navy, however, began permitting female officers to serve on submarines last year.

Military officials have said that they keep many positions off-limits because most women don’t have the same strength as men. But some female veterans questioned why the Pentagon has been slow to adopt gender-neutral physical requirements for such jobs. Maybe only a few women would qualify, they said, but they should be allowed to try.

“It takes training. Every athlete knows that,” said Anu Bhagwati, a retired Marine captain who served as a martial-arts instructor and held a black belt in close-combat techniques. “We want to do everything that the guys are doing, within limits. Not all of us want to be in the infantry, but not all the guys do, either.”

She said some of the resistance to change was cultural. The Marine Corps, she said, still segregates male and female recruits for basic training — the only service to do so.

After they join the Marines Corps, most male recruits “barely see another woman other than their wives or girlfriends,” said Bhagwati, who left the Marine Corps in 2004 and is now executive director of the Service Women’s Action Network. “They’re taught to believe that women are fat and lazy and will just get you in trouble.”

The Pentagon said it found no evidence that the existing job exclusions limited career advancement for women, contrary to assertions from some advocacy groups and members of Congress.

Women make up about 14 percent of the active-duty military but only about 7 percent of the roster of generals and admirals.

The armed forces have been making gradual progress on that front. The Air Force this month nominated Janet C. Wolfenbarger, a commander at Wright-Patterson Air Force Base, to become its first female four-star general.

Last year, the Marine Corps assigned Brig. Gen. Loretta E. Reynolds to become the first female commanding officer of its iconic recruiting depot on Parris Island, S.C. She had previously served as a commander in Afghanistan and Iraq.

Some military leaders have said it is only a matter of time before the remaining barriers for women are repealed.

Last month, Gen. Peter Chiarelli, the vice chief of the Army, told The Washington Post on the eve of his retirement that banning women from combat jobs was an anachronism.

“There is this mistaken belief that somehow through prohibiting women in combat jobs we can protect them,” he said. “I would rather have standards that we apply across the board.”