The next time the 80-year-old retired chemistry professor takes his protest to the plaza outside the federal courthouse in Manhattan, he may make it home without being locked up. A federal judge on Thursday ordered the dismissal of an indictment against the professor, Julian P. Heicklen, who had been charged with jury tampering for advocating the controversial position known as jury nullification while outside the courthouse.

Mr. Heicklen had repeatedly stood with a “Jury Info” sign and handed out brochures supporting nullification, the view that jurors who disagree with a law may ignore their oaths and vote to acquit a defendant accused of violating it. Prosecutors said such advocacy, “directed as it is to jurors, would be both criminal and without constitutional protections no matter where it occurred.”

But the judge, Kimba M. Wood of Federal District Court, wrote that a person violated the jury tampering statute only when he or she knowingly tried to influence a juror’s decision through a written communication “made in relation to a specific case pending before that juror.” Judge Wood added that she would not “stretch the interpretation” of the statute to cover speech that was “not meant to influence” a juror’s actions in a specific case.

Mr. Heicklen expressed pleasure at the ruling. “Not just for me,” he said. “I think it’s a major decision for the country.” He added: “This is better than having them throw me in jail.”

Mr. Heicklen had contended that he did not try to influence specific jurors; rather, he handed out brochures to anyone who passed by, hoping jurors were among them. Mr. Heicklen, who acted as his own lawyer, was assisted by two lawyers, Sabrina Shroff and Steven M. Statsinger of the federal defender’s office.

Ms. Shroff said she was pleased by the ruling. “The right to speech is just so fundamental,” she said. Prosecutors declined to comment on the ruling. In a hearing last month, a prosecutor called Mr. Heicklen’s advocacy “a significant and important threat to our judicial system.”

Judge Wood made it clear that the indictment could be dismissed merely on a reading of the plain language of the statute, which refers to trying to influence a juror through “written communication” in relation to an “issue or matter pending” before the juror. By taking that approach, the judge avoided First Amendment questions raised in the case, said Rachel E. Barkow, a law professor at New York University, who has written about nullification.

“I don’t think sensible prosecutors should have even brought this case,” Ms. Barkow said, adding that Judge Wood had rejected “the government’s broader reading because it would arguably chill protected speech.” Christopher Dunn, associate legal director of the New York Civil Liberties Union, said the ruling freed Mr. Heicklen to resume his activities outside the courthouse, at 500 Pearl Street.