Lt. Col. Oliver L. North's lawyer had objected to yet another question yesterday when an exasperated Senate Iran-contra committee Chairman Daniel K. Inouye (D-Hawaii) suggested North could take care of himself.

"Let the witness object, if he wishes to," Inouye told lawyer Brendan V. Sullivan Jr.

"Well, sir," Sullivan replied, "I'm not a potted plant. I'm here as the lawyer. That's my job."

If Sullivan were a potted plant, he would be a prickly pear.

While lawyers representing previous witnesses generally have sat quietly by their clients' sides, Sullivan has been a combative, tenacious and outspoken advocate for North.

He has accused the House and Senate select committees of engaging in a "stall job" designed to stretch North's testimony into next week, which Sullivan said would give committee lawyers the weekend to prepare additional questions; he shouted at the committees to "get off his {North's} back"; he bluntly warned the committees not to question North's wife, Betsy.

Despite frequent reminders by Inouye that, under congressional rules, the lawyer's role is restricted to advising his client, Sullivan has repeatedly objected to the conduct of the proceedings and to the questioning by House chief counsel John W. Nields Jr. and Senate chief counsel Arthur L. Liman.

Sullivan -- described by Inouye in an exchange Wednesday as "one of the best defense lawyers in town" -- is a partner at the prominent Washington firm of Williams & Connolly. Although they do not generally offer demonstrations of it on network television, the firm's lawyers -- and Sullivan in particular -- are known for their scorched-earth, no-holds-barred approach to litigation.

But lawyers who have watched the proceedings said Sullivan has a purpose in his protests.

He is trying, they said, to protect his client against the possibility of perjury charges by making certain the fired National Security Council staff aide is not forced to answer the same question repeatedly. He is also seeking to ensure that North gets to tell his own story as fully as possible, while presenting him as a lonely victim who is being unfairly attacked. And, they said, in heated moments, he is hoping to deflect attention from North to give his client more time to formulate answers.

"I think if Liman was representing North he'd be doing the same thing that Sullivan is doing," said Georgetown law Professor Samuel Dash, who was chief counsel to the Senate Watergate committee. "It's good trial tactics. You'd certainly do it in a courtroom. It's unusual to see it in a committee hearing. Sullivan is saying, 'I'm here and I'm going to represent my client as if I were in a courtroom.' "

Trial advocacy expert Irving Younger, a former Williams & Connolly partner, said Sullivan "is not concerned solely with this investigation. If that were all that was involved, I wouldn't be surprised if he weren't wholly cooperative." But with an indictment by independent counsel Lawrence E. Walsh looming, Younger said, "what you do really is destabilize the situation, just make trouble, so nobody quite knows what's happening. If you don't make trouble, all you're doing is turning your client over to law enforcement authorities that mean him harm."

Yesterday, Sullivan engaged in the legal equivalent of hand-to-hand combat with Liman, a partner at the New York law firm, Paul, Weiss, Rifkind, Wharton & Garrison, who is renowned as one of the country's foremost trial lawyers.

The battle with Liman was joined from his first question. Liman asked North if last Nov. 25, the day he was fired from the NSC, was one of the worst in his life. North waited to answer as Sullivan whispered in his ear.

"I wasn't asking whether it was one of the worst days in Mr. Sullivan's life," Liman said.

A few minutes later, they were at it again.

Liman was interrogating North about whether former national security adviser John M. Poindexter, who had been North's superior, had approved diverting profits from arms sales to Iran to support the Nicaraguan rebels.

"You seem to be hesitating," Liman said. "Is there any doubt in your mind?"

Sullivan jumped into the fray. "He's just looking for tricks, Mr. Liman," Sullivan said.

The legal dueling resumed when Liman asked North whether he was reading from prepared notes in answering questions about Poindexter's role in the diversion. "Don't tell him what it includes," Sullivan instructed his client.

After a debate about whether the papers were covered by the attorney-client privilege, the dispute continued.

Liman: " . . . Are you able to recall your conversation with Adm. Poindexter on the 21st without looking at that book?"

Sullivan: "That's none of your business either. You just ask him the questions."

Inouye: "Please address the chair."

Sullivan: "Mr. Chairman, let's get -- let's get to the substance of these hearings and stop trying -- get off his back."

Inouye: "We have a P.A. system here. You need not shout, sir . . . . Please proceed."

North: "Counsel, I would . . . "

Sullivan: "Don't answer the question. Next question, Mr. Chairman . . . it won't be answered."

Sullivan "sees himself in a hostile forum and has to stand in front of his client," said Robert F. Muse, who was a lawyer on the Senate Watergate committee and represents former Costa Rican ambassador Lewis A. Tambs in the Iran-contra inquiry. "Somebody's got to run interference for the client and make sure they don't gang up on him. It's healthy for the client, at least psychologically, to know that somebody's riding with him, and also you tell the opposing lawyer they're not going to get a free ride."

"He's talking to the television audience," Dash said of Sullivan's objections. "He's telling the people . . . 'Here I am with my hero client in his ribbons trying to tell the American people the whole truth and they're trying to bottle this up, to limit his answers, to drag it on, to harass him.' He's really trying to get a hearing from the public that the hearings are unfair and his client isn't getting a square deal."

Although the committees have given North so-called use-immunity -- meaning that his testimony or leads derived from it cannot be used against him -- North could be prosecuted for perjury if he lies to the select committees.

"Brendan has his eye on the doughnut, not the hole," said Richard Ben-Veniste, an assistant Watergate special prosecutor. "The doughnut is the trial, if there is one."