A federal judge yesterday dismissed five bribery charges against Dr. Murdock Head the Airlie Foundation director who is being tried for allegedly arranging payoffs to two congressmen and other government officials.

The dismissal of the five so-called illegal gratuity charges, nevertheless, left intact the principal conspiracy count on which Head is being tried before a U. S. District Court jury in Alexandria. Head is also charged with six counts of tax evasion and tax falsification.

The five counts dismissed yesterday by Judge Oren R. Lewis centered on allegations that Head, 55, had given an illegal $1,000 loan to a now-retired Internal Revenue Service agent. The prosecution contended that the loan was a payoff in exchange for an improperly lenient tax audit of Head's foundation, based in Warrenton, Va.

Lewis had hinted in July, shortly after Head was indicted, that he might dismiss the illegal gratuity counts -- the least serious of the charges lodged against the foundation director.

In dismissing the gratuity counts yesterday, Lewis ruled that the five-year statute of limitations had expired because the $1,000 loan was allegedly made in 1970. Prosecutors argued that the charges did not violate the statute of limitations because the loan was indefault and was not paid off until 1974.

Lewis rejected their contention, sayind, "You can go to the Court of Appeals on it."

Head, who is also a George Washington University professor and department chairman, is charged with conspiring to arrange $49,000 in bribes to Rep. Daniel J. Flood (D-Pa.), former Flood aide Stephen B. Elko and former Rep. Otto E. Passman (D-La.) in addition to the allegedly "laundered" $1,000 loan to the former IRS agent.

Despite his dismissal of the gratuity counts, Lewis said he would allow the $11,000 loan to the former tax agent to remain included as an alleged bribe in the overall conspiracy count. The prosecution contends that the bribes were given by Head in return for help in getting federal grants and contracts for his foundation as well as for an allegedly lenient tax audit.

Lewis previously had dismissed similar gratuity charges against Jesse P. Hare, the former IRS agent who allegedly received the $11,000 loan arranged by Head. Lewis had cited the same statute of limitations in dismissing the charges against Hare. The prosecution has appealed Lewis' ruling on Hare's indictment but prosecutors said they had not yet decided whether to appeal yesterday's dismissal of the counts against Head.

Lewis announced his decision to dismiss the gratuity counts against Head at the conclusion of the prosecution's case. Head's lawyers have said they wanted to call Hare, along with Flood and Passman, as defense witnesses in an attempt to dispute the allegations against Head, but they told Lewis yesterday that they had decided not to do so because all three men intended to invoke the Fifth Amendment.The Fifth Amendment allows witnesses to decline to give testimony that might incriminate them.

In contrast with Thursday's acrimonious court session -- during which Lewis sharply criticized the U. S. prosecotors -- yesterday's proceedings appeared relatively relaxed and subdued.

"The press takes a very jaundiced view of what goes on here. Let's today try to do it with a little bit of dignity and order," said Lewis, a colorful and controversial judge who will be 77 years old on Sunday. "I'm trying to keep everybody calm today," he added later.

Before completing its presentation of evidence yesterday, the prosecution produced a series of witnesses whose testimony appeared designed to corroborate several government contentions. Prosecutors have asserted that Head maintained a slush fund to pay bribes and that Head arranged to list phony expenses in the tax returns of a firm linked with Airlie Foundation to reduce the company's tax liability.

Raymond Garcia, president of the Raven's Hollow film-making firm affiliated with Airlie Foundation, testified that he had seen envelopes "crammed full of bills" -- including $100 bills -- in Head's private safe.

Herbert V. Frayer, a financial adviser to a Mellon family heiress, told the jury that he had received a $25,600 fee from Head even though Frayer said he had performed no consulting work for Airlie enterprises. Prosecutors allege this fee was improperly listed as an expense on Raven's Hollow tax returns. Frayer said the money was actually used to pay off a personal bank loan to him that Head had guaranteed.