Cheryl Piechowicz, 23, wife of a Prince George's County man who was gunned down April 28 in an underworld-style slaying at the Pikesville hotel he managed, testified in U.S. District Court today that the defendant in a drug conspiracy trial here was the man she saw in the hotel one night last November.

In the wake of the executions, Piechowicz, who said in an interview that the assassin's bullets were really meant for her, has been guarded by federal agents. Today, flanked by two guards, she testified that she was "100 percent positive" that defendant Anthony Grandison, 30, was the same man.

Federal prosecutors considered her testimony crucial because it placed the defendant in the Warren House Hotel at the same time a man, identified by authorities as Grandison, occupied a room in which a cache of heroin and cocaine were later found.

Grandison is charged with possession of a handgun and conspiracy to distribute heroin and cocaine. If convicted he could be sentenced to a maximum of 35 years in jail.

The trial took a dramatic turn two weeks ago when two prosecution witnesses, Scott Piechowicz, 27, and his sister-in-law, Susan Kennedy, 19, were shot to death at the hotel's front desk. Cheryl Piechowicz and Kennedy worked as desk clerks at the hotel but Cheryl Piechowicz was not on duty at the time of the killings. Grandison was in jail at the time of the killings.

Earlier today, federal prosecutors produced a surprise witness, who said he tested heroin for Grandison and rented a room at the Warren House Hotel for him Nov. 8 in exchange for $180 worth of the narcotic. Anthony Garrison, 34, a Baltimore postman and confessed heroin user, said he agreed last Friday to testify for the prosecution "because I was scared."

He said prosecutors offered him and his family protection and a letter to protect his job at the post office in exchange for the testimony.

In his opening argument Friday, defense attorney Edward Smith Jr. said he would present evidence to prove that Grandison was not the man who rented room 219 at the Warren House.

Today Garrison, who said he started using heroin in Vietnam in 1970, said that he acted as a guinea pig on a number of occasions to test the potency of heroin allegedly supplied to him by Grandison. Two guards stood nearby as Garrison testified that he rented the hotel room but did not enter it.

The prosecution also presented a Drug Enforcement Administration special agent and a DEA chemist, who testified that the narcotics found in an overnight bag in room 219 were of exceptionally high purity. Agent John Ryan said the 4 1/2 ounces of cocaine and four ounces of heroin had a total street value of $351,600.

Under cross-examination by Smith, Ryan said that five fingerprints were found on articles in two overnight bags but that they didn't match either Grandison's or Garrison's prints.

In a calm voice, Cheryl Piechowicz, looking occasionally in Grandison's direction, said Grandison entered the hotel last Nov. 9. She said her husband asked Grandison if boxer Sugar Ray Leonard had announced his retirement earlier that night. She said Grandison turned around and replied, "yes." She said Grandison was standing about 20 feet away at the time and that she remembered his face. She said she later identified Grandison from a set of photographs supplied by the FBI.

Grandison, in a blue jogging suit and tennis shoes and wearing gold colored bracelets, looked on impassively as she testified.

Because of publicity on the slayings, the 15-member jury is sequestered. Assistant U.S. Attorney Ty Cobb has not mentioned the killings during the trial. Tomorrow the prosecution is expected to read into the record testimony Scott Piechowicz gave at a hearing in March.