A federal judge denied yesterday defense requests that he dismiss key elements of bribery conspiracy and tax charges against Airlie Foundation founder Dr. Murdock Head as Head's trial entered its final stages.

The trial, in its fifth day, was recessed late yesterday by U.S. District Judge Oren R. Lewis after long closing arguments by attorneys for both sides. The jury is scheduled to begin deliberations this morning after receiving instructions from the judge.

In free-wheeling closing statements, federal prosecutors pictured Head as the "major domo" of Airlie, the "master plotter and master of detail" who had intimate knowledge of what they called "bizarre and squirrelly accounting methods" at the Airlie conference center near Warrenton, Va.

Defense attorney Frank W. Dunham Jr. characterized the government's case as "a bundle of pieces" that relies almost entirely on the word of a former congressional aide, Stephen B. Elko, who is a "convicted perjurer and felon, a consummate professional witness."

Head, 57, is charged with conspiring to bribe two former congressmen in an alleged attempt to influence government grants and contracts for the conference center. He also is charged with giving an illegal $1,000 gratuity to one of the legislators, former Rep. Daniel Flood (D-Pa.), and with criminal tax evasion involving an Airlie affiliate, Raven's Hollow, a filmmaking company.

Dunham asked Lewis yesterday to dismiss the gratuity charge, arguing that federal prosecutors had presented insufficient evidence to support the allegation and trying to cast doubt that the alleged offense occurred within the legal statute of limitations.

But David B. Smith, an assistant U.S. attorney on special assignment from the Justice Department's criminal appeals unit in Washington, contended prosecutors had shown a pattern of activities by Flood on Head's behalf, including a 1972 vote by Flood for $75 million in extra funds for the Agency for International Development to help fund a $5 million, five-year population control program at Airlie.

Lewis ruled it was up to the jury to decide whether the alleged offense fell within the five-year period covered by the gratuity law in this case.

A smiliar request by Dunham that Lewis dismiss from the jury's consideration two allegedly illegal tax returns filed on behalf of Raven's Hollow for 1974 and 1975 also was denied by the judge.

The statute of limitations has become a crucial element of the case. Head first was indicted in July 1979; he was convicted of conspiracy involving tax offenses in October 1979, but the conviction was overturned on appeal.

In the current trial, the so-called "overt acts" by Head that the government contends were illegal include only those that fall within the five years preceding Head's original 13-count indictment -- back to July 12, 1974.

Those three cats -- the two tax returns and the alleged gratuity given Flood -- are central to the prosecution's case; a ruling by Lewis to dismiss them would have been a major defense victory.