A lawyer for Lyndon H. LaRouche Jr. urged a federal appeals court here today to set aside a $202,000 damage award won by the NBC television network against the three-time presidential candidate and asked it to order a new trial in LaRouche's unsuccessful libel suit against the network.

But Floyd Abrams, representing NBC, said the unusual damage award against LaRouche was justified by "the degree and nature of the offensive behavior of Mr. LaRouche."

A three-judge panel of the 4th U.S. Circuit Court of Appeals heard the argument in an appeal by LaRouche of his unsuccessful libel case against NBC in federal court in Alexandria last year.

LaRouche, who lives on a heavily guarded estate near Leesburg, had claimed that NBC defamed him in two broadcasts that portrayed LaRouche as the anti-Semitic leader of a "violence-prone" political cult and charged that he at one time suggested the assassination of President Carter.

The jury in the nine-day trial, after rejecting LaRouche's libel suit, awarded $3 million in punitive damages and $2,000 in actual damages to NBC in its countersuit claiming that LaRouche followers played "dirty tricks" on the network by trying to sabotage one of its interviews for the controversial broadcasts. U.S. District Judge James C. Cacheris later reduced the punitive portion of the award to $200,000.

According to testimony at the trial, a person identifying himself as an NBC employe called the office of Sen. Daniel Patrick Moynihan (D-N.Y.) to cancel a scheduled interview with NBC, and a person identifying himself as a Moynihan aide telephoned the network to cancel the interview and to seek information about others contacted by NBC for the story.

LaRouche lawyer Robert Rossi told the appeals panel that there was a "total absence of any evidence to support the verdict" against his client for interfering with NBC's "business relationship" with Moynihan.

"The matter was cleared up within a very short period of time," he said. "The interview went ahead."

But Abrams cited, as damage to NBC, the time it took producer Pat Lynch and other employes for the "undoing of the dirty tricks that Mr. LaRouche engaged in."

"NBC has the right to expect that people won't go around saying they're NBC reporters when they aren't," Abrams said. He said that although he did not know of a similar verdict, "On the other hand, I don't know of anyone who behaves the way Mr. LaRouche does."

On the issue of whether NBC had libeled LaRouche, Rossi argued that the trial judge erred in refusing to compel NBC to reveal the identity of its confidential sources for the broadcasts and then permitting NBC employes to testify about what the confidential sources, identified as former LaRouche associates, had told them.

"They cannot refuse to reveal the sources and then get up at trial and say, 'Source X told me this, Source Y told me this, and Source Z confirmed this,' " he said. "To do so you might just as well repeal the libel law." Rossi said it would have been a "ludicrous burden" for LaRouche to try to discover the confidential sources himself by questioning all of his former associates.

Abrams contended, however, that LaRouche and his lawyers failed to make "the slightest effort" to uncover the sources on their own. The attempt to force NBC to disclose its sources, he said, was a "deliberate effort by Mr. LaRouche and his followers to harass NBC" for doing unfavorable stories.

A lawyer for the Anti-Defamation League of B'nai B'rith, which was a defendant in the libel case, asked the appeals court to overturn the trial judge's refusal to order LaRouche and his lawyers to pay the league's attorneys fees and other expenses for bringing the suit in an alleged attempt to "harass and intimidate" the league.

If the appeals court upholds the damage award against LaRouche, it is unclear whether NBC will be able to collect the money. LaRouche testified at the trial that he has had no income since 1972.