Attorneys for the families of two robbery suspects shot and killed by a so-called Prince George's County police "death squad" in 1967 told a federal court here today the men were the victims of "murderous force" and that the police acted as "judge, jurors and executioner."

In one case, Joseph D. Vasco Jr., then a detective and now a lieutenant colonel and second-highest official of the county police department, fired his shotgun from close range at a suspect already down and mortally wounded by police gunfire, the attorneys maintained. The shootings occurred during a holdup staged by police at a High's store in Adelphi.

Vasco "administered the coup de grace -- a shotgun blast in the belly," killing 18-year-old William Hunter Matthews of Takoma Park, said attorney R. Kenneth Mundy in one of several opening statements to a six-member civil jury.

Attorneys for Vasco and other county officials quickly challenged the account, telling the jury that Vasco fired at Matthews because the suspect was still reaching for a hair-trigger pistol knocked from his hand after he had been shot by other police.

The jury of three men and three women is hearing claims by the Matthews family and survivors of another man killed in a second robbery, as well as two other men arrested in the robberies, that the "death squad," as it was called in police circles, set up a series of phoney robberies and burglaries in 1967. The death of the other man, William C. Harris, 25, occurred during the Nov. 26 robbery of a Chillum 7-Eleven store.

Squad members pressured street informants to solicit associates to participate in the holdups, helped them select stores and businesses to "hit" and in one instance provided a "getaway" car and an inoperable shotgun for the informant, Mundy said.

Police then lay "in ambush" at the targeted stores and shot or arrested participants recruited by the informants, the attorney said. These procedures, he said, were approved by Prince George's County State's Attorney Arthur A. Marshall Jr., one of six defendants in the case.

The survivors contend that the police actions violated their 14th Amendment rights to due process; they have asked for damages totaling $9 million.

In the sometimes sharply worded opening statements today, defense lawyers denied that police staged the robberies and burglaries and described the participants in the incidents as experienced thieves who had a "predisposition" to commit crime.

"This is not a case involving constitutional rights or civil rights," said Prince George's Deputy County Attorney Michael O. Connaughton. "This is a case involving money" -- an apparent reference to the $9 million in claims against the county, Vasco, Marshall and other officials.

Attorney James P. Salmon, representing two alleged members of the "death squad," Capt. James Fitzpatrick and retired Lt. Blair Montgomery, said county police used informants in the traditional and proper manner, telling them "to go out and find what crimes were being planned and come back and tell the police about them" so that police could stake out the targeted stores.

The incidents occurred 15 years ago but did not come to public light until 1979, when a series of stories containing the "death squad" allegations appeared in The Washington Post. Judge Herbert F. Murray, who is presiding over the current trial, has ordered attorneys not to use the term "death squad" in the presence of the jury.