A mostly middle-aged Balitmore County jury acquitted 68-year-old Roman G. Welzant tonight of charges he willfully killed one teen-ager and seriously wounded another after his suburban Baltimore row house had been pelted repeatedly with snowballs one stormy night last January.

The verdict, which came shortly before midnight after more than 10 hours of deliberation, brought to an emotional close a trial in which Welzant became a symbol for the elderly of the suffering that can be inflicted on them by the young.

Welzant contended that the shootings were in self-defense and culminated a dozen years during which he and his wife had been harassed by generations of teen-agers in their suburban neighborhood of Eastwood. The jury chose to believe him and the legal battle is over. But the moral questions raised by "the snowball tragedy" are likely to be debated for some time to come.

As foreman George C. Smink, 64, a Westinghouse industrial engineer, rendered the jury's verdict on each of five counts, Frances Kahl, the mother of the slain youth began sobbing and was escorted from the courtroom crying, "You all have Albert's blood on your hands. Mr. Welzant, you're a killer."

Welzant hugged his son Robert and his wife Genevieve over the courtroom railing. "Thank God," she sobbed, stroking his hair. "I knew it. cI knew it."

About 60 persons were in the courtroom for the verdict, more than half of them reporters. Judge Austin Brizendine admonished those in the court, "there'll be no demonstration on the rendition of the jury's verdict." But he could not stifle the audible sighs of relief and outcries of despair.

Within half an hour of the verdict, the Welzants and two of their grown children were seated in defense attorney Russel White's Towson office, answering questions.

Roman Welzant said that he would not go back to the neighborhood where the case began. "We'll have to give up [the house]. I'll never feel the same in there anymore.

"It's been a sad time for everyone," he added. As for the jurors, he said that during the long hours of deliberations, while he sat in outer offices or paced the muggy corridors, "I just hoped they would recognize the truth."

Asked where they would go in the meantime, Mrs. Welzant said, "We have no plans. Nothing. No plans." Mrs. Welzant said that she did not know who Albert Kahl's mother was, and when Mrs. Kahl jumped up in the courtroom screaming at the jury and the defendant, Mrs. Welzant said she leaned over to her friend and asked, "Who was that?"

"I pray for her," Mrs. Welzant said later in reference to Mrs. Kahl. "I feel sorry for any mother that loses a son. Her heart aches. I wish her well."

White, Welzant's attorney, said he was surprised at the length of the deliberation. "Pent-up emotion drained out of me as soon as I heard the verdict," he said.

The prosecutors, meanwhile, congratulated the jury on the job they had done. Prosecutor Thomas Basham said he was sure they considered the years of harassment suffered by the Welzants since "it was in evidence. But you can't pick out one thing and say that's why they did what they did," he said.

Welzant was charged with second-degree murder, assault with intent to kill, assault and two handgun violations. If convicted on all counts, he could have received up to 90 years in prison.

The shooting of 18-year-old Albert Kahl and the wounding of his friend James K. Willey , 16, were a climax to what Welzant said was 12 years of harassment by several generations of teen-agers in Eastwood, a middle-class neighborhood of brick row houses just over the Baltimore line.

To Welzant, the youths were young hoodlums who had shattered his and his wife's dreams of a peaceful retirement. To the teen-agers, he was "the cameraman," a solitary figure who would emerge from his home and break up their gatherings and sometimes snap their picture.

From the beginning of the trial there was no question as to whether Welzant fired the shots that killed Kahl and wounded Willey. At issue were the events that led up to the shootings.

And that then became a question of whom to believe: Welzant, who said he was grabbed, tussled, thrown upon the ground and threatened or the teenagers who said he was never touched.

Also at issue, the defense and prosecution agreed, was whether Welzant had reason to fear for his life and could not have successfully retreated, or whether he in fact had provoked the final, fatal confrontation by emerging from his home, gun in hand, to stand his ground.

The case went to the jury of seven women and five men after five days of testimony, much of it emotional. Today, as on previous days, the court room was filled with elderly sympathizers of Welzant.

After 45 minutes of instructions from Judge Brizendine and three hours of closing arguments, the jury got the case at about 1 p.m.

An identification that the jury was having difficulty reaching a verdict came three hours later when it asked the judge to further define a particular criminal offense at issue. Judge Brizendine took the question in chambers and, according to courthouse sources, declined to answer, leading the jurors to ponder as best they could what was described as a technical question.

The jury continued deliberating throughout the evening, at one point sending out for dinner but not recesing. It returned its verdict at 11:37 p.m.

From the beginning, the prosecution faced the problem of making the case that whatever harassment there wad did not justify a human death. They also had to contend with a perception that parents and friends of the victims bitterly resented -- that if was somehow the victims who were on trial, not Welzant.

"He did something he thought would end his problems," Basham said. "Two wrongs don't make a right."

Basham began, "This is a case, ladies and gentlemen, which seems to touch something in all of us . . . While you may feel some sympathy for one side or another, set that aside."

"This case is not to be decided on emotion," agreed defense lawyer Russell J. White. "There is no great principle to be derived out of this case, regardless of the outcome."

Welzant testified he emerged from his modest end row house after two intense bombardments of snowballs and after police, responding to the first of four calls he made to them that night, said they could not arrest anyone without a positive indentification. Welzant said he went out into the snowy night to make that identification.

Basham suggested, however, the identification could have been made from inside with binoculars Welzant owned, that Welzant was upset with the police's refusal to make any arrests and that "he went out to end all this trouble."

After firing two warning shots, Basham said, recalling his witnesses' testimony, Welzant seemed almost to be challenging the youths to come toward him and fight.