Former national security adviser Robert McFarlane's "equivocal and confusing" testimony could help Oliver North in defending himself against charges that he lied to Congress.

The prosecution at North's Iran-Contra trial tried to pin McFarlane down Thursday on the question of who wrote two misleading letters to Congress.The letters in September 1985 carried McFarlane's signature, but North is accused of helping to prepare them. Three of the 12 criminal charges against North are that he obstructed Congress and made false statements in connection with the two letters.

Last Monday, McFarlane testified that he assumed it was North who prepared a draft of a letter to then-U.S. Rep. Michael Barnes denying National Security Council staffers solicited funds for the Contras or offered tactical advice. At the time of the letter, North - an NSC aide - was helping raise contributions and overseeing a secret military supply operation.

But on Tuesday afternoon, responding to questions from North lawyer Brendan Sullivan, McFarlane acknowledged he wasn't sure North had prepared the draft.

"I assume the prosecutors wouldn't show me something that wasn't true," he added.

"Is there anything to show that North had anything to do with it?" asked Sullivan.

"No," responded McFarlane.

On Wednesday morning, U.S. District Judge Gerhard A. Gesell declared that McFarlane had given "equivocal and confusing testimony." The question, said Gesell, is whether McFarlane or "his subordinate North was officially and knowingly responsible for specific activities attributed to North in the indictment."

On Thursday afternoon, prosecutor John Keker pressed McFarlane, who responded that North "was the only person who could have" written the draft of the letter to Barnes. McFarlane said that he had gotten a draft back and that "I started from something."

In connection with the other letter, to then-House Intelligence Committee chairman Lee Hamilton, McFarlane didn't dispute the suggestion by Sullivan that just two paragraphs written by North, for which he was not charged with a crime, ended up in the final version.

However, Keker brought out that North had reviewed a draft prepared by McFarlane, and made some changes but left untouched the denials regarding soliciting funds and offering tactical advice.

"You both knew you were doing something wrong," Keker told McFarlane in reference to the two letters.

"I knew I was withholding information," responded McFarlane. "He (North) was clearly concerned" about how to answer them.