A long-awaited "death squad" civil trial has begun in federal court here against Prince George's County State's Attorney Arthur A. Marshall Jr., two high-ranking county police officials and others accused of setting up a series of robberies in 1967 in which two persons were shot and killed by police.

The $10.5 million civil damage action brought by survivors of the slain men and by two men arrested in the incidents began Tuesday before U.S. District Court Judge Herbert F. Murray after months of tactical maneuvering by both sides.

Pretrial motions and procedural wrangling among the 11 lawyers in the complicated case have taken up the last two days, and a jury is not expected to be picked for the trial until Monday.

Scheduled to last four to six weeks, the trial will hinge on two 1967 incidents in which, plaintiffs said, a group of police officers known in police circles as the "death squad," recruited informants to solicit others to participate in robberies.

The informants then advised police of the robbery plans, and officers staked out the targeted stores, slaying one man and arresting one in each of the two incidents, according to the plaintiffs' attorneys. Police then falsified reports to conceal their actions, the lawyers said.

All of this in turn was known and authorized by Marshall and Benjamin R. Wolman, then an assistant to Marshall, according to the plaintiffs.

Such actions--generating robberies, using deadly force to stop them and falsifying police records -- violated the plaintiffs' right to due process under the 14th Amendment of the U.S. Constitution, the plaintiffs said.

The defendants--Marshall, Wolman, police Lt. Col. Joseph D. Vasco, Capt. James Fitzpatrick, and former police officer Blair Montgomery -- denied they asked informants to solicit would-be robbers. They contended just the opposite: that the informants came to them and told them of planned robberies. They denied falsification of records.

Lawyers for plaintiffs said the two incidents cited in their case were not isolated but were part of a pattern of unconstitutional actions, with at least three other set-up robberies from mid-1967 until the end of that year. There were no fatalities in the other incidents, they said.

In the first fatal incident on June 9, 1967, at a High's store on Riggs Road in Adelphi, William Hunter Matthews, 18, of Takoma Park was shot and killed by officers in a stakeout after he had been recruited by informant Gregory Gibson to participate in a holdup there, plaintiffs' lawyers said. Another participant allegedly recruited by Gibson, Marvin Rozier, was arrested at the scene.

In the second incident, William Clyde Harris was shot and killed during an attempted holdup of a 7-Eleven store on Chillum Road in Chillum on Nov. 26, 1967, according to plaintiffs' attorneys. The lawyers said informant Sydney Hartman had recruited both Harris and David E. Wedler for the holdup. Wedler was arrested at the scene.

The plaintiffs' lawsuit was filed after allegations about the "death squad" first surfaced in The Washington Post in 1979 and a subsequent investigation by the state police concluded the holdups had been "instigated."