William F. Buckley Jr., the quipful conservative columnist, was on the witness stand. Mark Lane, the frequently firebrand lawyer, was asking questions.

But these two celebrities had spent more than a day in tedious cross-examination in U.S. District Court here, and finally an elderly juror fell asleep yesterday with a toothpick in his mouth. Later, a U.S. marshal dozed off too.

After a 10-minute break, called by Judge Joyce Hens Green so those in the courtroom could "stretch and throw some water on our faces," Lane resumed his prowl through almost 40 years of the National Review, the conservative magazine that Buckley edits, as trial of the magazine's $16 million libel suit against the right-wing Liberty Lobby continued.

Questioning Buckley before a six-member all-black jury, Lane, representing Liberty Lobby, confronted him repeatedly with quotations from the magazine criticizing Adam Clayton Powell, the Rev. Martin Luther King Jr. and the Rev. Jesse L. Jackson.

He picked out phrases from old issues -- "Koon Klux Klan," referring to the Black Muslims in 1960; "The Jig is Up, Baby," referring to a federal tax investigation of Powell in 1956, and "doggerel inaugural," referring to Jackson's campaign for president in 1984. Lane suggested they were offensive to blacks and read from a dictionary to try to prove it.

Buckley said emphatically the words weren't meant that way.

Later, under questioning from his own attorney, J. Daniel Mahoney, Buckley said that he and Jackson had discussed writing a book together several years ago. Buckley also read from an article he wrote in 1969, saying the United States needed to elect a black president by 1980.

At one point, Lane introduced a joke from a 1967 National Review about "Uncle Cornpone" and suggested it was an example of antiblack humor.

Buckley rejoined, "Uncle Cornpone is what we referred to Lyndon Johnson as. He's not black, Mr. Lane. Sorry about that."