A puerto Rican once held in a Viet Cong jungle camp with Marine Pfc. Robert R. Garwood testified today that a feast and ceremony staged by their communist captors marked Garwood's "liberation" as a POW and his alliance with the Viet Cong.

After the May 1967 ceremony, Luis Antonio Ortiz-Rivera testified, Garwood moved out of the prisoners' compound, lived in a hut occupied by guards and left the camp occasionally.

Ortiz-Rivera, 34, took the stand on the sixth day of the Marine Corps hearing to determine if Garwood should be court-martialed on charges of desertion and collaboration with the enemy. The charges, both carrying a death sentence upon conviction, were filed last March, when Garwood returned to the United States after 13 1/2 years in Vietnam.

The testimony by Ortiz-Rivera, a former specialist 4 held for two years by the Vietnamese communists, was the most definitive to date in the hearing.

The 33-year-old Garwood, from Adams, Ind., disappeared in 1965 while working as a jeep driver near Da Nang. The Marines allege that Garwood became a deserter between March and June 1967.

Ortiz-Rivera, the sixth survivor of the jungle camps to testify, said through an interpreter that he and other POWs also were treated to "liberation" ceremonies in the camps near the Laotian border as their captivity neared an end.

Under cross-examination, he said speeches were made by the Viet Cong and their American and South Vietnamese prisoners, that soon-to-be-released men wore red sashes during the ritual, and that they feasted afterward on meat, "which was something we never had."

But he added that only Garwood stayed in the prison camp area after his ceremony.

"He stayed in camp, but he stayed in the area where the guards were at," Said Ortiz-Rivera.

Afterward, he said, Garwood often visited the other prisoners in their compound and chatted with them. "He wanted to know how we were doing, and he would counsel us to do everything" the Viet Cong "told us to do" Ortiz-Rivera said.

Ortiz-Rivera, who joined the Army in 1966, was in a camp with Garwood for about seven months in 1967.

His testimony shifted the time focus of the Article 32 hearing, the military equivalent of a grand jury.

When the hearing convened last month, other former POWs testified that during 1968 and 1969 Garwood acted as an interpreter for the Viet Cong in the camps, that he carried a gun and lived as a comrade among his captors.

The hearing was recessed over the holidays, and resumed Tuesday.

Marine prosecutors expect to finish their case by Saturday.

Attorneys for Garwood then will have the option of presenting witnesses, but his chief lawyer, Dermot Foley, has given no indication of his plans.

When the testimony is concluded, the hearing officer for the case will decide whether to recommend a court-martial.

Garwood has been assigned quarters and a job as a mail clerk at Camp Lejeune, where he was stationed upon his return to the United States. But he lives most of the time with a family active in POW-support efforts in the Jacksonville, Fla., area.

He is the second former Vietnam POW to face possible court-martial. Charges of collaboration were filed against a Marine sergeant in 1973, but were dismissed.