The White House said yesterday that Ursula Meese, wife of Attorney General Edwin Meese III, was fully within her rights when she wrote a letter to a federal judge asking for leniency for a Tennessee congressman's son who was awaiting sentencing on a tax-fraud conviction.

White House spokesman Marlin Fitzwater said, "She's a citizen. And she's free to express her feeling in any case that she wants to, to use any name that she wants to." In the letter, reported yesterday in The New York Times, Ursula Meese also cited her husband's admiration for Joe S. Duncan, son of Rep. John J. Duncan (R-Tenn.). Referring to the attorney general, Fitzwater said, "He has a right to personal opinions, and she has a right to express them."

The Times said Ursula Meese wrote to Judge R. Allan Edgar of Chattanooga, Tenn., on June 17 urging "very favorable consideration" for Joe Duncan, who is a friend of the Meeses' niece. "My husband, Ed, and I consider Mr. Duncan to be an outstanding, conscientious and sensitive young man," she said in the letter. "He is a man who shows a great deal of integrity and a person we personally respect and admire, particularly in his handling of these long drawn-out court proceedings."

Defending Ursula Meese, Fitzwater said, "She's a citizen and she's free to express her feeling in any case that she wants to, to use any name she wants to.

"She has a right to say anything she wants to in a personal letter to the court. That's what freedom of speech is all about in this country. How can you question it?" Fitzwater asked.

Justice Department spokesman Terry H. Eastland said yesterday that the attorney general did not know about his wife's one-page letter until after it was sent. Eastland said that Ursula Meese wrote the letter as an individual, not in her capacity as wife of the attorney general.

"He {Meese} didn't know anything about it. As soon as he learned about it, he immediately recused himself. And {Deputy Attorney General Stephen S.} Trott immediately told the relevant prosecutors just to ignore the letter," Eastland said.

Although there was no indication that any law or regulation was violated by the letter, legal ethics experts said the attorney general's name should not be used to attempt to affect the outcome of a case his department prosecuted.

Eastland said that Attorney General Meese has met Joe Duncan a "few" times.

Duncan was convicted last May of filing a false tax return. Last July, the Justice Department recommended a prison sentence of three years and a "substantial" fine. The maximum fine in the case would be $100,000.

In August, Edgar sentenced Duncan to three years in prison, with all but six months suspended, a fine of $3,000 and 400 hours of community service. Edgar refused to discuss the case.