Anthony Grandison, the 30-year-old Baltimore man whose trial on drug charges here created a sensation last month when two prosecution witnesses in the case were shot to death, was found guilty today of possession of a handgun and possession with intent to distribute narcotics.

As the verdict was read in U.S. District Court 90 minutes after the jurors started their deliberations, Grandison, dressed in tennis shoes and a burgundy jogging suit, remained motionless, smiling only faintly.

Reached by telephone moments after the verdict, Cheryl Piechowicz, the 23-year-old wife and sister of the two slain witnesses, said she was "ecstatic. Justice was done. One down, one to go," she said, referring to the ongoing investigation of the gangland-style slayings of her husband and sister.

U.S. Attorney J. Frederick Motz, in a rare public statement, told reporters on the steps of the federal courthouse here that the verdict "clearly demonstrates that the judicial process cannot be aborted by those who would seek to undermine it by acts of force and violence."

Meantime, Grandison's attorney, Edward Smith Jr., said he would immediately file a motion for a new trial at the Fourth U.S. Circuit Court of Appeals in Richmond.

Today's verdict came just 13 days after Scott Piechowicz, 27, and his sister-in-law Susan Kennedy, 19, were gunned down at the Pikesville hotel where they worked. Both had been scheduled to testify at the Grandison trial. The killings attracted so much media attention on the trial that Judge Joseph C. Howard sequestered the jurors. Although the slayings occurred before the jury was picked, no testimony linked the killings to the trial.

Piechowicz' wife, who contended that the executioner's bullets were meant for her, was put under federal guard in the wake of the shootings. In testimony earlier this week, flanked by federal agents, she linked Grandison to the Warren House hotel room in which a handgun and a cache of cocaine and heroin valued at $351,600 were later found.

"I was petrified," she said today, referring to her stay in the witness stand. "The only thing that kept me going was thinking about Scott and Sue. I knew I had to do it." She said she heard of the verdict while lunching with her parents and Scott's at a downtown restaurant. She said they shared her elation.

Pretrial testimony of Scott Piechowicz was read to the jury. Defense Attorney Smith said he would appeal the verdict on grounds that that testimony should not have been admitted. He also charged that federal authorities violated search and seizure rules in their investigation.

"Mr. Grandison just feels we have good grounds for a new trial," Smith replied, when asked why Grandison smiled upon hearing the verdict.

The closing arguments in the case produced a contrast in style between Smith and Assistant U.S. Attorney Ty Cobb, who called Grandison a "high-roller" and "master of manipulation."

"Who creates heroin users? People like Anthony Grandison, a drug dealer who has a different designer jogging suit for every day and gold all over his body," Cobb said to the jury.

Smith, meantime, calmly recited folksy homilies and lessons from classical literature in an attempt to sway the jury. He attempted to belittle a crucial prosection witness, Anthony Garrison, the 34-year-old Baltimore postman who testified that he rented the hotel room for Grandison in exchange for two bags of heroin.

Garrison agreed to testify only after federal authorities offered him and his family protection and a letter to protect his job. Smith told the jury Garrison was a man of "scruffy reputation" who merely wanted to "hush-puppy his way back to the post office."

In his post-verdict statement, Motz thanked all the witnesses who testified, "particularly Mrs. Piechowicz, who had the courage to stand up for that which is right."

Judge Howard set June 13 for sentencing. Grandison could receive a maximum of 35 years in prison.

An FBI spokesman, meanwhile, said an investigation into the hotel murders is continuing.