James Dao / New York Times News Service

In the fall, two freshly minted female lieutenants joined about 100 men in Quantico, Va., for one of the most grueling experiences that soldiers not in war can experience: the Marine Corps’ Infantry Officer Course.

At the 86-day course, candidates haul heavy packs and even heavier weapons up and down steep hills, execute ambushes and endure bitter cold, hunger and exhaustion. Uncertainty abounds: they do not know their next task, or even how long they will have to perform it. At IOC, calm leadership under duress is more important than physical strength, although strength is essential.

One of the women — the first to enter the course — was dropped on the first day, with about two dozen men, during a notoriously strenuous endurance test. But the second woman lasted deep into the second week, when a stress fracture in her leg forced her to quit.

“She was tough,” Gen. James Amos, the Marine Corps commandant, said of the woman, who is now at flight school. “She wasn’t going to quit.”

Amos hopes the experiences of those women, and others to come, will provide crucial clues about the future of women in the infantry, a possibility allowed by the recent lifting of the 1994 ban on women in direct combat units.

For the Marine Corps, probably more than any other military service, gender integration is a difficult affair. Not only is the corps the most male of the services, with women making up only about 7 percent of its ranks, but it is also a bastion of the infantry. Nearly 1 in 5 Marines are “grunts,” proud of their iconic history of bloody ground battles, from Belleau Wood to Iwo Jima to Chosin Reservoir to Fallujah.

Not surprisingly, the idea of women in the infantry draws sharp questions from many active-duty Marines and veterans, who express concerns that standards will be diluted for women.

In an interview, Amos acknowledged hearing those worries, and insisted that the corps would not lower its standards. To guarantee that, he plans to use the course, which Marines consider the gold standard of infantry training, to study the performance of potential female infantry officers, and then use that data to develop requirements for enlisted infantry Marines.

In March, two Naval Academy graduates will become the second set of women to enter the course. Over the coming years, Amos is counting on dozens more female volunteers to provide him with enough information to decide whether women can make it in the infantry. The outcome, he says, is far from certain.

“I think there is absolutely no reason to think our females can’t be tankers, or be amtrackers, or be artillery Marines,” he said, referring to tracked amphibious assault vehicles. “The infantry is different.”

Indeed, Amos said, if too few women are able, or willing, to join the infantry, he or his successor may ask the defense secretary to keep the infantry closed to women. The deadline for that request is January 2016.

“You could reach the point where you say, ‘It’s not worth it,’” Amos said. “The numbers are so infinitesimally small, it’s not worth it.”

Advocates for women in the military would almost certainly protest any effort to keep the Marines infantry male-only. Those advocates acknowledge the harshness of infantry life: carrying heavy loads on foot for long distances and enduring spartan environments are requisite. But they say that properly trained women will make it through IOC and, eventually, whatever program the corps creates for screening and training enlisted infantrywomen.