A battle over the constitutional right of states to impose a moment of silence in public schools opened in U.S. District Court here today. The case, which pits the American Civil Liberties Union against the New Jersey Legislature, is seen by other states as one way of circumventing the U.S. Supreme Court prohibition against prayer in public schools.

Maryland, Virginia and 17 other states have laws providing for some form of silent meditation in the classroom. Most have not been challenged in court. However, in recent cases, such statutes have been struck down in Tennessee and New Mexico and upheld in Massachusetts.

The court cases come at a time of increasing pressure on Congress by conservative activists and fundamentalist churches to enact a constitutional amendment allowing prayer in public schools. According to a Gallup Poll released Sunday, 81 percent of Americans favor such an amendment, a finding consistent with earlier polls.

In July, the Senate Judiciary Committee sent two versions of a proposed prayer amendment--one backed by President Reagan that would allow audible prayer, another that would permit silent prayer or meditation--to the floor. Neither version is given much chance of passage because of filibuster threats in the Senate and opposition in the Democratic-controlled House.

Attorneys for the New Jersey Legislature, which enacted its law in December over the veto of Gov. Thomas H. Kean, argued today that the statute is "neutral" because it makes no mention of prayer. It says public schools "shall permit students to observe a one-minute period of silence to be used solely at the discretion of the individual student, before the opening exercises of each school day for quiet and private contemplation or introspection."

However, the outcome of the case may turn on the intent of the legislators who sponsored the bill, many of whom have sponsored more explicit prayer bills in past years. The courts have ruled that such laws must reflect "a clearly secular legislative purpose" to pass constitutional muster.

ACLU attorney Richard M. Altman, representing several students, parents and a teacher in the challenge to the law, argued that it was passed with "the singular purpose of reintroducing prayer into the public schools . . . it is a subterfuge for avoiding the Supreme Court ban . . . ." Newspaper reports quoting legislators were introduced as evidence.

"Who's to know what those boys and girls are doing during that moment of silence?" asked one state senator during the veto-override debate. "Maybe they're praying. I hope so."

Among the plaintiffs attending the opening of the trial today were Jean Ross, a Princeton attorney, and her son, Damon, 11.

"A minute of silence doesn't prove anything for people who are not religious," Damon said. "I don't believe in religion and I don't want to start believing."

Another plaintiff, Mark Tulloss, 13, said that after the law began to be invoked at his junior high school in Roosevelt, his teacher "let slip the word prayer. People didn't like that. Everybody in the class thought it was wrong."

Jeffrey May, a teacher from Kendall Park, said he decided to file suit after officials at his high school threatened him with dismissal for refusing to enforce the law. The moment of silence, he said, would be "perceived by students as a religious ceremony" and has "no educational benefit."

Another plaintiff, Cary Butler, 17, was temporarily suspended from Hillsborough High School last year for refusing to participate.

Testifying today, Langdon Gilkey, a University of Chicago theology professor, said the law would be interpreted as religious by students and teachers and "force them into a situation where it would be uncomfortable for a number of them if they don't pray."

However, attorney William W. Robertson, representing the legislature because New Jersey's attorney general refused to participate, said the law would create no more divisiveness than the current practice of allowing Jewish children to wear yarmulkas in class.

The law "is not a violation of the Constitution so long as it does not tell them to pray," he said.

Maryland's 1964 law allows schools to require students "to meditate silently for approximately one minute . . . . During this period a student or teacher may read Holy Scripture or pray." In Virginia, a 1976 law allows schools to "establish a daily observance of one minute of silence . . . to the end that each pupil may . . . meditate, pray or engage in any other silent activity . . . ."