The prosecution rested its case in the conspiracy retrial of Dr. Murdock Head yesterday as federal Judge Oren R. Lewis refused to rule out significant portions of the government's case against the former Airlie Foundation director.

Defense attorney Frank W. Dunham Jr. did get Lewis to strike from the jury's consideration any acts mentioned in Head's indictment that occurred before June 17, 1974. The judge held that a five-year statute of limitations barred the government from prosecuting Head for anything that occurred then.

The 59-year-old Head's 1979 conviction on a single count of conspiracy involving tax infractions was overturned by a federal appeals court last February because Lewis failed to instruct a jury about the statute of limitations.

Head, who holds degrees in law, medicine, and dentistry, is on trial for allegedly conspiring to bribe former representative Daniel J. Flood (D-Pa.) and Otto E. Passman (D-La.) with $49,000 in cash payments that were supposedly funneled through a congressional aide. Head also is charged with givng an improper $1,000 gratuity to Food through Stephen B. Elko, a former congressional aide, and conspiracy for tax infractions involving a motion picture company affiliated with his Warrenton-based foundation.

Arguing that there was not "a scintilla of evidence" presented that showed Head "signed, prepared or sent" improper 1974 and 1975 tax returns for the film company, Dunham also moved to strike those allegations and the charge that Head gave an improper gratuity to Flood through the aide. a

But Judge Lewis denied the motions on the gratuity count saying the jury had "plenty of evidence" on which to base a verdict. " . . . I acquitted him on six different counts [on the original 1979 indictment] because I believed there wasn't enough evidence. I won't do that here." Lewis also denied a motion to dismiss the conspiracy charges. $ lewis kept open the possibility of striking Head's 1974 and 1975 tax returns from the indictment. Following yesterday's proceedings, the trial will be recessed for a week to allow Lewis to attend a judicial conference.

Dr. Phyllis Piatro, who worked on a population project for Head at George Washington University, testified that Head once told her that "There were several congressmenm who would do anything he asked."

But defense lawyers suggested that Piatro resigned from her position in a department run by Head when he refused to giver her a raise. Dunham and his colleague Mark Cummings also attacked the credibility of a key prosecution witness, Diane Kidwell, with testimony from one of her former workers, Carol Fleshman, Kidwell had testified Thursday that she gave Head cash that she received from inflated expense advances she was told to prepare.

"She [kidwell] said she had been fired," Fleshman testified, "'I'll get even with him [Head],' Diane said very bitterly."

Cummings and Dunham also pursued their case by producing evidence that prosecution witness Norvel James, a former accountant for Head, falsified documents for his own personal benefit and used an Airlie credit card to buy gasoline while on vacation.

Judge Lewis, who earlier attacked the prosecutors' handling of the case, yesterday stopped testimony from two FBI agents, a move that disturbed both the prosecution and defense, when it became clear that both agents had to refer to reports of their interviews with Elko.

Lewis argued that the interviews did not constitute a statement taken under oath by a qualified stenographer when that it would be unfair to allow the agents to read "a lot of hearsay" into the trial record.