New York ? Jurors at the Martha Stewart trial will have to grapple with two distinct images of the government’s star witness: Was he a star-struck liar, or an impressionable young man caught up in someone else’s crime?

The competing perceptions put forth by lawyers in the case will be pivotal as former Merrill Lynch & Co. brokerage assistant Douglas Faneuil takes the witness stand, probably beginning today.

Prosecutors say Faneuil passed a tip from broker Peter Bacanovic to Stewart on Dec. 27, 2001, that the family of ImClone Systems founder Sam Waksal was trying to dump the stock.

Stewart sold her ImClone shares that day, just before it plummeted on a negative Food and Drug Administration report on an ImClone cancer drug.

Faneuil, then 26, initially supported Stewart and Bacanovic’s account that they had a pre-existing arrangement to sell the stock when it fell to $60. Now he supports prosecutors’ version — and will be the linchpin of the government’s case.

“I think his youth helps the government,” said David Berg, a Houston white-collar attorney. “And the fact that he was trying to preserve his job. It’s the good-little-soldier scenario.”

But even before Faneuil testifies, defense attorneys for Bacanovic and Stewart tried to punch holes in his credibility, devoting parts of their opening statements to portraying him as a liar.

Bacanovic’s lawyer, Richard Strassberg, went so far as to describe Faneuil as “fixated” by Martha Stewart, bragging to friends about even the most casual contact with her at Merrill Lynch.

Strassberg suggested that Faneuil, hoping to impress Stewart, decided on his own to tip her about the Waksal sales.

“He did it because he was trying to be the big man,” Strassberg said. “He did it out of inexperience, he did it out of foolishness. But he did it — not Peter.”