Dr. Murdock Head, claiming prosecutors interfered with his defense, failed yesterday to persuade a federal judge to block his retrial on charges that he engaged in a criminal conspiracy.

Head, founder of the Airlie Foundation in Warrenton, Va., testified in federal district court in Alexandria that a handwritten note from a District prosecutor to his lawyers provoked a dispute over legal fees that hampered his efforts to defend himself. But Judge Oren Lewis, who presided at Head's initial trial two years ago, rejected his claims about the note.

"Jim, read it and weep!!!! Or, in view of your client's resources, reap!!" it read.

Written by prosecutor Mark Touhey and sent to Head's lawyer, James Sharp, the note was attached to a copy of a related indictment that preceded one charging Head with 13 counts of tax evasion, bribery and conspiracy. Head, a lawyer, surgeon, and dentist, later was convicted on one count of conspiracy involving tax infractions and sentenced to three years' imprisonment.

By the time of his trial, Head and Sharp had severed their relationship because of a dispute over fees.

Yesterday Head testified that the dispute was caused, at least in part, by the federal prosecutor's note and was evidence of improper conduct by the Justice Department. That misconduct, Head's current lawyers contended, should be ground for rejecting the department's plans to retry Head, whose conviction was overturned last year by an appeals court.

Sometime soon after the related indictment of former representative Daniel J. Flood (D-Pa.), Head said the law firm of Sharp and Randolph asked for payment of $150,000. Head said he could not raise the money and was forced to dismiss the law firm, which had spent months preparing his defense.

Judge Lewis, however, rejected Head's request to block his retrial, but not before the 79-year-old jurist flustered lawyers on both sides, provoked frequent courtroom laughter and generally lived up to his nickname of "Roarin' Oren."

"It was an unconscionable fee for something you hadn't even been indicted for yet," said Lewis, referring to the demand for $150,000 two months before Head's indictment. Lewis ruled that the note sent from Touhey to Sharp did not constitute government interference. "It wasn't an official government act. I find there was no prejudice."

A spokesman for Sharp, Randolph and Green, as the law firm is now called, later disputed Lewis' characterization of their fee as "unconscionable" and said the amount was "in no way influenced" by Touhey's note.

The 4th Circuit Court of Appeals ruled in February that Lewis failed to properly instruct the jury that convicted Head. While the appeals court found fault with Lewis, the white-haired judge whose courtroom performances are legend in Alexandria, was hardly in an apologetic mood yesterday.

"If I make an error a second time, so be it," said Lewis. "That's what they have a court of appeals for."

The original indictments returned against Head in the fall of 1978 were based primarily on testimony by Stephen Elko, a former administrative aide to Flood. Elko testified that Head had arranged to pay $49,000 in bribes to Flood, former representative Otto E. Passman (D-La.) and himself between 1971 and 1974 in exchange for help in securing federal funds for his foundation and an affiliated department at George Washington University Medical Center.

But the jury that convicted Head apparently did not believe the testimony of Elko, a convicted felon and perjurer. They did not convict Head of bribery, but rather found him guilty of one count of participating in a conspiracy centering on tax infractions, including arranging an improper $11,000 loan to a former Internal Revenue Service agent.

Yesterday Judge Lewis was scornful of both the defense attorney's motions and the government's ability to prosecute the case. Lewis characterized some of defense lawyer Frank Dunham's motions as "picayune" and frivolous." But he tried to comfort Dunham by suggesting that if the second trial goes against Head, there would likely be grounds for appeal.

"I'm gonna let the government fall flat on its face," chuckled Lewis. "They're very good at making mistakes."