As the Prince George's County police "death squad" trial enters its fifth month in federal court here this week, a core question still curls through the millions of words of testimony: Did police "create" a string of crimes in 1967 and then illegally kill, wound or arrest the unwitting perpetrators?

One of the longest and most fiercely fought civil rights trials in recent Maryland history, the $9 million lawsuit has pitted a ragged array of ex-street informers, petty thieves and a lone retired policeman against a somber parade of county officers in blue-gray uniforms and business suits.

They have made accusations, issued denials, waffled under cross-examination, pleaded ignorance or contradicted themselves and others on a bewildering variety of points. But it all still boils down to the crucial issue: Did police instruct informers to solicit acquaintances to commit five robberies and burglaries of convenience stores where waiting officers then shot and killed two suspects, wounded another and arrested seven more?

"These crimes were police-created crimes, and the deaths, injury and arrests flowed illegally from them," argued Barnet D. Skolnik, one of four attorneys for survivors of the slain suspects and other plaintiffs against the police and county government for alleged violation of civil rights.

"This is not a case involving civil rights," retorted Deputy Prince George's County Attorney Michael O. Connaughton in opening statements to the jury. "This is a case involving money"--an apparent reference to the $9 million in damages the plaintiffs hope to split among themselves if they win the case.

Police acknowledge the shootings and arrests and even occasional suggestions to informers to change the time and location of holdups to protect the public.

However, they vehemently deny directing informers to recruit friends for the crimes. Rather, they say, the informers came to them with tips on planned holdups and burglaries, and detectives then staked out the targeted stores in routine fashion. Police say they fired in self defense only after pistol-wielding suspects ignored warnings to halt and fired at officers.

A crucial element in the trial is the credibility of the police against the credibility of ex-informers. Will the jury accept the words--often disputed by police--of admitted housebreakers and hustlers, who acknowledged living in the informer's twilight zone of evasions and street-level gamesmanship with both their criminal colleagues and the police?

Take Sidney Hartman, an ex-informer who faced assault and check forgery charges in 1967. He told the jury that police pressured him to get two acquaintances to rob a 7-Eleven store. One of the acquaintances was shot and killed by police, the other arrested.

"I did it to save my a--," Hartman told the jury. "I was stacking 'em up . . . , throwing 'em to the wolves."

At stake in the trial are the futures of three current or retired county police officials--the defendants in the case--who are accused of masterminding the so-called "death squad" incidents 15 years ago.

The defendants include Lt. Col. Joseph D. Vasco Jr., now the second-highest-ranking official in the police department. He was considered by many to be a shoo-in as chief of the 900-member force until survivors of the "death squad" incidents filed their $9 million lawsuit in 1980. Now his future is no longer so certain.

The other two defendants are Capt. James Fitzpatrick, currently commander of the major crimes division, and retired Maj. Blair Lee Montgomery, who now lives in Florida. At the time of the 1967 incidents, Montgomery was a lieutenant in charge of a detachment of detectives in the department's Hyattsville substation. Vasco and Fitzpatrick were rank-and-file detectives under Montgomery's command. All three are expected to testify on the incidents later in the trial.

Two additional defendants--Prince George's County State's Attorney Arthur A. Marshall Jr. and former Assistant State's Attorney Benjamin R. Wolman--were cleared of liability in the case last month when presiding Judge Herbert F. Murray ruled that the plaintiffs had failed to prove that the two prosecutors had acted "in concert" with police in the incidents.

While the so-called "death squad" incidents occurred 15 years ago, the plaintiffs did not file their lawsuit until 1980, after The Washington Post first brought the "death squad" allegations to public light in a series of articles in 1979.

The trial started Nov. 15 before Murray and a six-member civil jury here and is expected to last about another month. It is recessed this week while Murray presides over an unrelated trial.

Attorneys for the plaintiffs, now battling an array of police witnesses for the defense, rested their case on Feb. 28. During almost three months of testimomy, the plaintiffs attempted to portray Vasco, Fitzpatrick and Montgomery as skilled manipulators of local petty criminals whom they pressed into service as informers in exchange for reducing or dropping court charges against them.

So far, five informers have testified, an assortment of reluctant and sometimes embittered witnesses, all dragged under subpoena into court from prison or self-imposed anonymity. Two have insisted on using pseudonyms to protect them from possible reprisals by criminal acquaintances.

In their testimony, they told a tangled tale of two loosely acquainted groups of youths--one black, one white--who were responsible for many of the convenience store holdups and break-ins in the Hyattsville area in 1967. They said police, under community pressure to curb the crimes, cultivated a number of the youths as informers.

But Vasco, Fitzpatrick and Montgomery took it one step further, several of the informers said, and pressured them to invite acquaintances to rob or burglarize certain stores. Police in several instances then selected the time and date of the crimes, the informers said, and waited for the unwitting participants to arrive. In one instance, it was claimed, police provided the informer and his companions with a getaway car.

When the robbery or burglary actually occurred, the informers said, police shot or captured the suspects and let the informers go.

The only informer to testify on behalf of the police, a 34-year-old man using the pseudonym Sandy Stillwell, has denied that police asked him to recruit participants for crimes.

However, outside the presence of the jury, plaintiffs' attorney Skolnik said Stillwell told him he did not want to testify because of fears of reprisals and if compelled to testify, he planned to lie and "might act crazy" on the witness stand.

Stillwell started testifying late last week and will continue when court recovenes next week.

Police defense attorneys Edward P. Camus and James P. Salmon, while denying that police "orchestrated" the 1967 crimes, acknowledge that police sometimes suggested alternative times and locations to informers who came to them with tips about planned crimes. The attorneys said police suggested late night hours or remote stores to minimize the chance of innocent bystanders being caught in a possible cross-fire between suspects and waiting police.

Besides merely instructing informers to recruit participants for crimes, plaintiffs' attorneys Skolnik, R. Kenneth Mundy and Charles L. Richards contend, police gratuitously shot and killed two suspects at the targeted stores where concealed detectives "lay in ambush."

The first fatal incident occurred June 8, 1967, during a holdup at the High's Dairy Store at 9101 Riggs Rd. in Adelphi. In that shooting, Vasco fired his shotgun at William H. Matthews, 18, seconds after another officer had shot Matthews during the holdup.

Mundy said Vasco stood at close range and delivered a coup de gra ce to the already wounded Matthews.

Police witnesses countered that Matthews, who was armed with a hair-trigger .32 caliber pistol, aimed at the head of a policeman who was posing as a clerk in the store and then turned and fired at another officer when he was ordered to halt. Matthews was then hit by shotgun fire, they said, and Vasco shot him a second time as Matthews was crawling to retrieve the pistol knocked from his hand by the impact of the first shotgun blast.

Police attorneys also introduced medical and ballistics evidence that they say showed Vasco was 10 to 16 feet away from Matthews when he shot him. Plaintiffs' attorneys contend he was much closer.

The second fatal shooting happened during a Nov. 26, 1967, stake-out of a 7-Eleven store at 1331 Chillum Rd. in Chillum. Lt. Thomas F. Taylor, who is not a defendant in the trial, testified he killed robbery suspect William Clyde Harris, 25, to protect a fellow officer. Taylor said that one of the men fleeing from the store, later identified as Harris, turned and pointed a pistol toward another officer with his arm almost fully extended after being ordered to halt. At that moment, Taylor said he fired his shotgun, striking Harris in the back and right arm, killing him.

Mundy confronted Taylor with a physician's report indicating that one of the pellets from Taylor's shotgun had entered the back of Harris' upper right arm above the elbow and exited from the front or "dorsal aspect" of the lower arm below the elbow.

Asked by Mundy if the path of the pellet was "more consistent" with Harris' arm bent in a "pumping position," as though he were running, rather than extended fully, Taylor said, "Yes, . . . that would be a possible option."

Plaintiffs contend the physicians's report shows Harris was killed, not as he was aiming his pistol at police, but as he was fleeing from them.

The circumstances of the two fatal shootings and the recruiting of criminal participants by informers, plaintiffs say, violated the suspects' civil rights and denied them due process under the 14th Amendment. Police have repeatedly denied the recruitment allegation. They also contend that under departmental guidelines in 1967, police could fire their weapons either to stop a fleeing felon or to protect themselves or others--circumstances that existed in the two fatal incidents.