The Marine Corps today opened a hearing to determine whether former prisoner of war Pfc. Robert R. Garwood should be court-martialed on accusations that he deserted to collaborate with his Vietnamese captors.

The Article 32 hearing -- roughly the military equivalent of a civilian grand-jury -- ended an eight-month investigation into charges leveled against Garwood by fellow Vietnam POWs.

After brief procedural steps, the hearing recessed until Dec. 18, when military prosecutors will present 15 witnesses against Garwood. Most of them are expected to be men who were held captive with Garwood in North Vietnam.

They have accused Garwood, 33, of donning a North Vietnamese uniform, goading American troops to throw down their weapons, mistreating American prisoners and acting as an interpreter-guide for North Vietnamese soliders.

Some of Garwood's accusers have conceded that they went beyond the traditional "name, rank and serial number" response to the North Vietnamese in order to survive.

Dermott Foley, of New York, Garwood's civilian lawyer, has indicated that concession will be a cornerstone of his defense. Garwood's only crime, Foley says, was to survive for 13 1/2 years after disappearing from his Marine unit Sept. 28, 1965, near Da Nang.

Garwood, of Greensburg, Ind., sat erect in a short-sleeved uniform during the brief hearing today, appearing far less gaunt than when he returned to the United States in March after slipping a note to a visitor that he wanted to come home.

He has been working as a mail clerk at this sprawling Marine base on North Carolina's southeastern coast since his return. Although two of the charges against him can carry a death sentence, he has been free to move about at will.

The Article 32 hearing for Garwood is expected to end in January, after a Christmas recess. The hearing officer, Maj. T. B. Hamilton Jr., will then recommend to the Camp Lejeune commander, Maj. Gen. David B. Barker, whether Garwood should be tried on any or all of seven charges against him.