Marvin P. Rozier, who has accused a so-called "death squad" of Prince George's County police of luring him into a staged robbery in 1967, acknowledged in federal court today that he participated in the holdup voluntarily, despite his earlier contention that he did not want to.

"You already testified that you never intended to go through with the robbery, didn't you?" asked Edward P. Camus, one of several attorneys representing police in a $9 million civil rights case here.

"Yes sir," said Rozier.

"But you took that trip to High's dairy store, target of the robbery of your own free will?"

"Yes sir."

"And did you attempt to get out of the getaway car on the way?"

"No sir."

"And if the robbery had succeeded, you expected to share in the proceeds?"

"Yes sir."

As it turned out, police were waiting at the store on Riggs Road in Adelphi on June 8, 1967. They interrupted the holdup, arresting Rozier, shooting and killing William Hunter Matthews, 18, and allowing a third participant, police informant Gregory Gibson, 18, to escape.

Rozier, members of Matthews' family and other plaintiffs sued police and two other Prince George's County officials for $9 million, accusing them of staging or authorizing not only the High's robbery but four other holdups and burglaries in 1967. They accused police of directing informants to recruit participants for the crimes and staking out the targeted stores with police.

In all, police killed two men, wounded a third and arrested another seven in violation of their civil rights, according to the plaintiffs.

Today, police attorneys continued cross-examining Rozier, trying to portray him as a street-wise hustler and undermine his contention that he was a reluctant and frightened youth cajoled into the High's holdup by informant Gibson.

Rozier acknowledged that he was familiar with guns, stole cars and participated in at least one armed robbery before the High's incident.

Attorneys for police contend such admissions show Rozier had a "predisposition" to engage in crime and thus was not innocently entrapped in the High's incident.

Attorneys for Rozier and other plaintiffs, however, argued earlier that the predisposition of participants was irrelevant since the police action of recruiting them in the first place was an unconstitutional deprivation of civil rights. Police have denied instructing informants to recruit participants.

The civil trial is expected to last another six weeks. The accused members of the so-called "death squad" include Lt. Col. Joseph D. Vasco Jr., now the second-highest ranking official of the county police department, Capt. James Fitzpatrick and retired Lt. Blair Montgomery.