Gen. Robert H. Barrow, a former drill instructor who was the point man for reforming the training practices of the Marine Corps, has been nominated by President Carter as the new Corps commandant.

The White House announced Barrow's selection yesterday. The 57-year-old four-star general will succeed marine Commandant Louis H. Wilson on July 1 if confirmed by the senate-a virtual certainty.

Barrow fought in three wars, starting in 1942 when he enlisted in the Corps and served briefly as an assistant drill instructor oat the same San Diego boot camp where the beating of a young recruit decades later brought an overhaul of Marine training.

Nicknamed "Louisiana" during his enlisted days, after his home state, Barrow went through officer's candidate school, winning his commission in 1943. He was sent to China during World War II, where he fought alongside Nationalist Chinese against the Japanese.

During the Korean War, Barrow was a captain in command of a rifle company that saw hard combat. He won the Silver Star in 1952 for braving enemy fire and taking an exposed position where he could direct his company's attack against the enemy.

A few months later, Barrow won the Navy Cross-second only to the Medal of Honor-for wresting the high ground away from the enemy to enable the 1st Marine Division to move through a Korean pass with light casualties.

His Navy Cross citation credited Barrow with helping "immeasurably in ensuring the safe passage of he 1st Marine Division through this hazardous pass."

During the Vietnam war, he was a colonel in command of the 9th Marine Regiment, which fought in the northern sector of South Vietnam in 1969 during Operation Dewey Canyon. The Army awarded Barrow the Distinguished Service Cross for his performance in Vietnam.

While highly decorated for his leadership in combat, Barrow belies the caricature of the bellowing Marine. He is a soft-spoken, compassionate officer who once listened sympathetically while one of his riflemen in Korea told him he could not fight anymore. Barrow said he understood, and made the Marine a medic.

Barrow was the Marines' manpower chief in 1976 when brutal training practice came to light, including a Parris Island, S.C., drill instructor accidentally shooting a Marine recruit through the hand while hazing him, and a high school dropout, Lynn McClure, being fatally beaten in the San Diego boot camp.

Wilson turned to Barrow to implement a series of training reforms, including "hands-off" warnings to drill instructors, a larger training role for officers and more freedom for recruits.

While Marine traditionalists grumbled, Barrow told anyone who would listen that the changes did not mean the Corps was going soft, but was instead eliminating the excess stress that had nothing to do with making a good soldier.

He winced as court-martials and congressional hearings revealed brutality in recruit training and fraud in enlisting Maines, once telling a reporter that "the Marine Corps itself is on trial."

But Barrow believes that the Corps has cleaned up its recruti training, thanks to Wilson's leadership and is more ready for combat today than at any time in its peacetime history.

"The Marine Corps isn't anything if it isn't ready," Barrow said once. He is expected to continue Wilson's stress on readiness.

Barrow is slated to take over as the 27th commandant at a time when the 187,000 member Corps is in transition. The Pacific, the Marines' World War II battelground, has faded as U.S. policymakers concentrate their main efforts on beefing up NATO and searching for ways to influence events in the oil-rich Third World.

Barrow believes the Corps, with its mobility and punch, could play a vital role on the flanks of NATO and in the Mideast if war came. He recently served as commander of the Marine's Atlantic Force and is currently assistant commandant.

Barrow and his wife, the former Patricia C. Pulliam, have five children. CAPTION: Picture, GEN. ROBERT H. BARROW . . . decorated veteran of three wars