Frances Kahl asked for a drink of water, but it was of no help as she tried to describe the night her 18-year-old son was killed.

"Please take me out of here, take me out of here, please," she pleaded at last to prosecutor Thomas Basham, who draped an arm around her shoulder and escorted her from the courtroom today. "Oh my God, oh my God," she cried as she left.

Her son, Albert Kahl Jr., died on the snowy night of Jan. 4 from a single bullet fired into his heart by Roman G. Welzant, who had also wounded 16-year-old James K. Willey only moments before. On those facts, there is no dispute.

But the shootings came at the end of a long night of terror during which the Welzant house was repeatedly bombarded by snowballs, and it also followed more than a dozen years of harassment of the proud and fiesty Welzant by generations of neighborhood youths in the working-class Baltimore suburb of Eastwood.

And so the slight, white-haired, 68-year-old Welzant -- to many now a symbol of the indignities inflicted by the young upon the old -- went on trial here this week for what the state alleges was murder and assault with intent to kill and what he maintains was self defense.

The testimony began today after three days of jury selection from a panel of 165 in the nationally publicized case dubbed "The Snowball Tragedy" by the Baltimore News-American and featured in a recent issue of People magazine.

It is, prosecutor Dana Williams told the sequestered jury yesterday "a tough case. The defendant is a sympathetic figure, to say the least."

In an unusual opening statement, Williams condemned the behavior of his star witnesses the night of the shootings, calling it "obnoxious, immature, unreasonable, unacceptable . . . everything they did was incriminating."

Welzant, the prosecutor said, "had good reason to be mad" but the youths' taunting, harassisng behavior "did not necessitate his shooting them."

"I think you're gonna find these boys believable," Williams said. "They were an average group of boys from an average community out celebrating on a Friday night, participating in what they considered childish pranks . . . they weren't really considering the defendants' feelings."

Over all the years, Welzant could never identify the youths who pelted his beloved home with snowballs, eggs and stones, breaking his windows, littering his yard, disturbing him night after night with boisterous drinking and loud obscenities. And, although they were his neighbors and many attended the same church, the teenagers never knew his name either. They called him simply "Camera Man," -- a solitary figure who often emerged from his home to snap their pictures and give them hell.

But neither Welzant nor his wife Genevieve ever "did anything to provoke the harrassment" his lawyer, Russel J. white, said yesterday, "They had an impeccable reputation as peaceful, quiet, honest neighbors."

White described the couple to the panel of mostly middle-aged and elderly jurors as "senior citizens" who "had led an almost exemplary existence all their lives. "They are good decent people, the type you'd welcome in your neighborhoods, living next to you."

That night, White said testimony would show, "they felt like the house was coming down" and Mrs. Welzant, "scared to death," went upstairs and prepared to flee out the window.

Welzant, who called the police four times that night, emerged from his house twice carrying a .22 caliber pistol he had purchased 10 years before but never used. Accounts sharply differ concerning the second confrontation that ended in the shootings.

White said that Welzant will testify he was grabbed by the youths and, believing "he's gonna be stomped to death," fired in self defense.

Willey, the first youth shot, testified today he never "grabbed Welzant. Another youth testified that Kahl moved toward Welzant after his friend had been shot but did not strike or attack the man.

The teen-agers admitted they had been drinking beer that night, but denied that any of the group was drunk. The defense said the autopsy would show that Kahl was "very very drunk."

Frances Kahl, the dead boy's mother, vividly recalled the evening from the witness stand -- how her husband fretted over Albert not wearing boots in the snow, how she waited up for her son's return and how, finally she learned the worst when her husband weent to fetch Albert from a neighbor's house.

"My husband came in the front door and screamed 'Albert's dead. He's dead. I can't bring him back no more.'"

Willey, by then, lay on his living room couch next door to the Kahls' house, a bullet lodged in his back. Why had they cursed the man and thrown snowballs at Welzant's house that night? he was asked yesterday.

"We just did it for spite because we knew he didn't like that," Willey testified. "We thought it was funny."