The smokeless-tobacco product-liability lawsuit brought by the family of Sean Marsee against United States Tobacco Co. went to the jury today after lawyers for the two sides sharply criticized each other in closing arguments.

Sean Marsee, who had been a high school track star in Ada, Okla., began to use snuff when he was 12, was found to have tongue cancer at 18, underwent surgery in hopes of stopping the cancer from spreading, and died at 19 in early 1984. His mother Betty Marsee seeks $146.6 million in compensatory and punitive damages from U.S. Tobacco, which makes the Copenhagen brand of snuff the youth used.

Company lawyer Alston Jennings accused George W. Braly and Dania Deschamps-Braly, the husband-and-wife team representing Betty Marsee, of "abuse" and "humiliation" of experts who testified for the defense that smokeless tobacco had not caused Sean Marsee's death.

George Braly accused defense lawyers, who included Oklahoma City Mayor Andy Coates, of deceiving their own witnesses. He said they did this partly by leaving it to him and his wife to break the news that U.S. Tobacco had known since 1974 of the presence in its snuff products of high levels of potent cancer-causing substances called nitrosamines.

After Jennings called the nitrosamine issue "an out-and-out smokescreen," Braly said that "the smoking gun in the hand of U.S. Tobacco" is nitrosomorpholine, a nitrosamine found to cause tongue cancer in rats. He said defense experts were startled to learn of this on cross-examination.

Deschamps-Braly said Sean Marsee died "tragically and pitifully," and charged that what U.S. Tobacco did to him and his mother was "an enormous evil."

Jennings accused her of appealing to the jurors' "emotions and sympathy" rather than focusing, as he said he did, on the scientific evidence.

District Judge David L. Russell spent 17 minutes instructing the six jurors -- four women and two men -- who began to hear evidence a month ago today. The jury -- the first to try a smokeless-tobacco product-liability case -- was sent home after deliberating for more than four hours.

To return a verdict for Betty Marsee, Russell said, the jurors must find unanimously, by "a preponderance of the evidence," that Sean Marsee's use of U.S. Tobacco's Copenhagen snuff caused his death. He defined the quoted phrase as that evidence which in your minds is most convincing and is more probably true than not true."

The punitive award sought by Betty Marsee, $136.5 million, would equal U.S. Tobacco's net income before taxes in 1983, the year in which Sean Marsee's illness was diagnosed. The number is "big enough to get their attention," Deschamps-Braly said, pointing out that the Greenwich, Conn., company's 1985 earnings were the highest as a share of sales (19.5 percent) of any Fortune 500 company.

"I imagine Mrs. Braly thinks money is everything," Jennings said. He accused her of portraying U.S. Tobacco as "a soulless, heartless corporation" and told the jurors -- as did the judge later -- that the law requires them to accord identical treatment to a corporation and an individual.

On behalf of Betty Marsee, the Bralys argued that testimony from outstanding experts provided "overwhelming" evidence that snuff caused Sean Marsee's fatal tongue cancer. For U.S. Tobacco, Jennings emphasized that there was no abnormality whatsoever at the site where Sean Marsee kept the cut of tobacco -- between the right cheek and gum.

George Braly accused company Chairman Louis F. Bantle and Vice President for Research and Development Richard A. Manning of "hiding in company headquarters" because they chose to testify in videotaped depositions that were played for the jury rather than to appear in the courtoom.

Braly noted that the only executive in the courtroom was one with no expertise in health and safety, Walt Garrison, a regional vice president and a former Dallas Cowboys running back. Throughout the trial, Garrison sat at the defense counsel table with the round outline of a snuff can visible on his left seat pocket.

Braly recalled the minutes of a 1968 company meeting in which Bantle, then vice president for marketing, was quoted as saying that "we must sell the use of tobacco in the mouth and appeal to young people. . . . We hope to start a fad."

He said Manning engaged in evasive "snuffspeak" in testifying that he did not know the nicotine levels in his company's snuff products and did not know the meaning of the words "safe," "dangerous" or "carcinogen," which is something that causes cancer.

Braly also reminded the jury that U.S. Tobacco put health warnings on the snuff it sold in Sweden, as required by health authorities there, while not giving Americans health warnings or even telling them there was a scientific controversy about the safety of snuff. This was "absolutely unforgivable," he said.