William S. Farmer Jr., the chief prosecutor in the Whitworth case, believes that being a federal prosecutor "is the best job a lawyer can have."

A banker's son who grew up in the South but fell in love with San Francisco "after having taken one cable car ride," Farmer, who is known as "Buck," started in the San Francisco office of the Justice Department's antitrust division, working on oil mergers and timber bid-rigging cases.

He switched to the U.S. attorney's office in 1979 in order to get more trial experience, but he still likes to handle complex cases. "The quick case, the routine stuff is not so much a challenge because . . . one person's dope case is going to look like another person's dope case," said Farmer, a graduate of Princeton University and the University of Texas Law School.

Farmer, 44, who is being assisted at the trial by Assistant U.S. Attorney Leida B. Schoggen, worked on the espionage case against James Harper, an electronics engineer who helped his wife sell stolen documents from a Palo Alto, Calif., defense contractor to Polish intelligence agents. Harper pleaded guilty in 1984 and was sentenced to life in prison.

But the most memorable of the cases handled by the U.S. attorney's office during Farmer's six years there was one that involved him a bit too personally.

Farmer was sitting in his office one day in 1982, he recalled, when "just on a whim" he chose to accept a collect telephone call from an inmate at Lompoc Prison. Farmer had successfully prosecuted a Colombian cocaine dealer, Jose Robert Gomez-Soto, who was serving time at Lompoc.

The inmate caller, Leon (Magic) Colburn, told Farmer that Gomez-Soto was plotting to assassinate Farmer, the federal judge who had sentenced him, several witnesses and federal agents.

"Magic" was supposed to be the hit man, and the FBI arranged to have him cooperate, but there were some nerve-racking days, Farmer recalled, "when I was worried to death that 'Magic' wouldn't be taken out of prison and Gomez-Soto would go through some other line of communication [to arrange the hit] and we wouldn't know anything about it."

The plot was foiled, and Gomez-Soto and his son were eventually convicted of conspiracy to murder, but "it was a harrowing experience," Farmer said. "At the time I didn't appreciate the fact that I was scared."