Three days after a Montgomery County police officer and a security technician were shot to death at a catalogue store in Silver Spring last month, detectives received a phone call that led to the arrest of six suspects in the case, according to testimony yesterday at a court hearing.

That call was from Janet Stringer, a friend of a girlfriend of one of those allegedly involved in the W. Bell Co. burgulary March 27 that resulted in the double slaying, Det. Harry Harner testified at a preliminary hearing in Bethesday District Court.

Stringer said that her friend, Valerie Lawson, had confided in her that her boyfriend was the "signal man" for the burlary, Harner recounted.

"Lawson trusted Stringer," Harner told Judge Leonard Rubin. "She had told Stringer of her boyfriend's criminal activity in the past."

But the trust that those now charged in the case had in each other and in their other friends was broken time and time again as law enforcement officials pressed their investigation.

Two of those arrested, Lawson and Herbert Smallwood Jr., alleged to be one of the two lookout men, have agreed to testify against the others in plea-bargaining agreements.

Lawson was accused of knowing the burglary plans in advance, providing a car used in the crime and harboring her boyfriend, Burl Courtnery, afterward. cCharges against her have now been dropped in return for her cooperation.

Smallwood was charged with two counts of murder, burglary, and armed robbery in connection with the case, but he will plead guilty only to one count of armed robbery in return for his testimony, according to his attorney, Thomas Abbenante.

Smallwood, of Southeast Washington, testified at yesterday's preliminary hearing for two defendants in the case, Courtney and James Arthur Calhoun, 27, one of the two alleged gunmen.

The court session lasted nearly eight hours and was said to be one of the longer such hearings held in the court. At its conclusion, Judge Rubin ruled that there was sufficient evidence to hold the two men and for the case to go to the grand jury for possible indictments. The judge ordered Calhoun and Courtney held without bond.

According to testimony from both Smallwood and Det. Harner, Calhoun and a man named Curtis Wayne Monroe entered the store about 6:30 a.m. by using an ax to smash through the roof as lookouts in separate cars near the catalogue store.

The intention, Smallwood said, was to wait for the manager, force him to open the safe and escape with the money, which they figured would be about $100.000. In fact, only $6,000 was found, according to Smallwood.

When the store manager, Douglas Cummins Jr., 28, entered the store, he was accompanied by a policeman, Philip Metz, 33, and an employe of the burglar alarm company, David Wayne Myers, 30.

Calhoun, who was in his an office where the store's safe was located, shot Metz twice in the head, while Monroe shot Myers once in the chest and once in the back, according to Harner's testimony, which he said was based mostly on an account by Cummins. Then Monroe shot Cummins once and Calhoun forced him to open the safe, Harner testfied.

After getting the money from the safe, Calhoun and Monroe escaped through the roof and ran to Smallwood's car, Smallwood testified, and they were then driven to the home of another friend, Otis Anderson, who has been charged with being an accesory after the fact in the case.

While driving to Anderson's apartment, Smallwood told Calhoun and Monroe that he wanted to stop to buy cigarettes and "Wayne [Monroe] said, 'f --- that, we killed them people back there'" Smallwood testified. We didn't stop for cigarettes," Smallwod said.

Courtney, Calhoun and Monroe are all charged with felony murder. If convicted, each could be sentenced to die in Maryland's gas chamber.