In a church jammed with more than 1,000 spectators and nearly a dozen television cameras, three Supreme Court justices sat stoically behind cardboard nameplates yesterday and issued an unprecedented opinion. It was unanimous. They said the plays and sonnets of William Shakespeare were written by a guy named William Shakespeare.

And above the resounding cheers of the standing-room-only crowd gathered to watch the moot-court debate about the authenticity of Shakespeare's claim to fame, Supreme Court Associate Justices William J. Brennan Jr., Harry A. Blackmun and John Paul Stevens suggested words of caution.

At best, they agreed, their decision was little more than the Supreme Speculation of the Land.

The debate, organized by American University and sponsored by university trustee David Lloyd Kreeger, took place in the Metropolitan Memorial United Methodist Church, adjacent to the university's campus on Nebraska Avenue in Northwest Washington.

The justices heard an hour of argument from two professors of American University's Washington College of Law.

Representing Shakespeare, James D.A. Boyle told the justices that the dramatist and poet was indeed the author of every work that bears his name, and that opposing views are based on an "enormous chain of assumptions" that sustain no merit under scrutiny.

Representing Edward de Vere, the 17th Earl of Oxford and the latest -- and apparently most legitimate -- challenge to Shakespeare's authorship, Peter A. Jaszi told the justices that Shakespeare was merely an uneducated theater patron who sold his name to the nobleman de Vere, who was forced by Queen Elizabeth to use a pseudonym for his work.

The rapid-fire debate was filled with slings and arrows of historical evidence from both sides.

Jaszi contended that it was simply impossible for a unlearned commoner such as Shakespeare, who never traveled to European cities, to have written the more than 36 plays attributed to him -- many of them set in foreign countries and all of them rich with sophisticated vocabulary.

He suggested, instead, that the author was de Vere, an aristocrat who had studied and traveled throughout Europe.

Jaszi pointed to character similarities between de Vere -- the subject of an 892-page book by Elizabethan scholar Charles Ogburn that has brought new spark to the authenticity debate -- and Hamlet.

He stressed that there were no obituaries or any other evidence of public mourning when Shakespeare died in 1616, "and certainly you would expect that kind of reaction to someone who is the greatest playwright in the history of the English language."

Boyle countered, saying Shakespeare was educated at the esteemed Stratford grammar school and that he was likely well-versed in legal terms of the day.

"His father appeared in court 67 times," Boyle said. "Even then, it was a very litigious society."

Debate persists on the authenticity of Shakespeare's name, Boyle suggested, simply because so little is known of Shakespeare's character.

"We don't know what kind of man he was, and we long to know," he said. "That longing makes us want to substitute a man we know much more about. And it is a short step from wish to deed."

The justices, who announced their opinions three hours after the professors completed their arguments, supported Boyle's defense, but said their views should not be taken as the last word in the debate, which began in the 19th century under the skeptical prodding of literary heavyweights such as Ralph Waldo Emerson, Henry James and Mark Twain.

"I don't think the contrary view is totally frivolous," Stevens said. "I have lingering concerns, and gnawing uncertainty about the matter. If the author of these works is not Shakespeare of Stratford, then de Vere is by far the strongest candidate."

Brennan contended that Shakespeare was hardly the "ignorant butcher's boy" that Oxfordians often make him out to be. He said Shakespeare's father was prominent in local affairs, and that Shakespeare received a good education. And he stressed that the Oxfordian case collapsed on one particular point: the inability to prove that de Vere, who died in 1604, wrote the handful of Shakespeare plays that were not published and performed until after that year.

Kreeger, who told the crowd he sponsored the debate because of his passion for Shakespeare's works and the merits of the authenticity issue, said the three justices were initially hesitant to participate when he approached them with the idea in the spring.

"But they became fascinated with it once I explained that serious students of literature had very grave doubts, and that this case really lent itself to legal analysis," Kreeger said.

More than 200 spectators had to be turned away, and nearly 100 reporters were on hand, including journalists from Canada and Great Britain.

"That's very satisfying," said Jaszi, who took the defeat nobly. "It would have been nice, of course, to win. But it was more important that this debate finally be taken seriously by the public. And that's clearly what happened."