For 9 1/2 hours over two days, in the privacy of a small jury room in Alexandria's federal courthouse, 12 jurors had debated the fate of Dr. Murdock Head, the Airlie Foundation director charged with scheming to bribe two congressmen.

But when the jury's guilty verdict was announced, one extraordinarily significant detail remained a closely guarded secret: The jurors had concluded that Head was not guilty of arranging to bribe either Rep. Daniel J. Flood (D-Pa.) or former Rep. Otto E. Passman (D-La.)

Throughout their lengthy debate and repeated votes on the charges lodged against Head, the jurors agreed not to rely on the testimony of a key prosecution witness, former Flood aide Stephen B. Elko, who had recounted a series of incidents in which he allegedly collected payoffs from Head.

weighing Head's testimony against Elko's, the jurors quickly decided it was a tossup -- an unreconcilable dispute between two men with little evidence to corroborate eigher verison of events.

"Who knows if Elko was really telling us everythin?" at least one juror is reportedly said to have wondered as the trial progressed.

The seven men and five women on the jury did, indeed, vote unanimously to convict the 55-year-old Head of a single conspiracy count, but they interpreted the conspiracy charge for more narrowly that was alleged in Head's indictment.

Instead of finding Head guilty of scheming to bribe Flood and Passman, the jurors convict the Airlie chief of participating in a conspiracy centering on what they regarded as tax infractions, including arranging an improper $11,000 loan to a former Internal Revenue Service agent.

The jury's reasoning in reaching its verdict has previously remained unclear because of a series of instructions given to the jurors by U.S. District Court Judge Oren R. Lewis, who presided during Head's trial.

The controversial 77-year-old judge told the jurors that they could interpret the conspiracy count against Head in several different ways. Under another interpretation, the judge said the jury might find him guilty of an illegal tax conspiracy.

In their written note to the judge last Friday afternoon, the jurors said only that they had found Head guilty of conspiracy. The note gave no clue to the reasons for their decision and did not indicate whether they believed Flood or Passman was implicated in the conspiracy. Lewis warned the jurors, moreover, that they were prohibited from publicly disclosing what transpired in the jury room.

Nevertheless, The Washington Post has pieced together an account of the jury's deliberations from information that became available during the four days since the verdicts were announced.

What is clear from this account is that the federal prosecutors failed to prove their central allegation against Head -- the charge that Head arranged to pay $49,000 in bribes to Flood, Passman and Elko in exchange for help in securing federal funds for the Airlie Foundation.

In trying to prove this allegation, the prosecutiors relied heavily on testimony by the soft-spoken Elko, who said he received the cash payoffs from Head during a series of furtive meetings between 1971 and 1974 at Airlie headquarters near Warrenton, Va.

Elko testified that he delivered $28,000 in bribes to Flood, turned over another $12,000 to Passman, and kept $9,000 himself.

Elko, however, is a convicted perjurer -- currently on parole from a two-year prison term stemming from a California bribery scheme. Elko testified as a prosectuion witness in Head's trial under a grant of immunity from further prosecution. The jurors were fully aware of Elko's criminal record -- a point emphasized by Head's lawyers in their arguments to the jury.

Elko's testimony, moreover, was verhemently disputed by Head, Airlie's founder and executive director. Head, who also hold positions as a George Washington University professor and department chairman, testified in his own defense that he had given comparatively small amounts of money to Elko during the early 1970s, but insisted that these payments included only legitimate political campaign combributions and one personal loan.

Agreeing not to rely on either man's account, the jurors quickly turned their attention to other issues -- the allegedly illegal $11,0000 loan from Head to former IRS agent Jessee R. Hare along with complex tax matters involving allegedly "back-dated" leases, a so-called "slush fund."

The jurors were experienced, articulate men and women, many of whom hold responsible jobs in businesses and government agencies. Eleven jurors were 36 years old or older. The 12th was 28. They included a sales manager and other sales persons, computer specialists and administrators. The foreman, William T. Lincoln, was identified as an electronic engineer for a public broadcasting operation.

On Thursday, the first day of deliberations, the jurors quickly voted to acquit Head of two tax-evasion counts. These counts alleged that Head attempted to evade income taxes owed by Raven's Hollow Ltd., film-making company linked with Airlie. In presenting these two charges, the prosecution had contended that Raven's Hollow fraudulently evaded more than $9,000 in taxes in the company's 1974 fiscal year and over $6,000 in taxes in 1975.

The jurors believed, however, that the alleged tax violations hinged on such small amounts of money that they did not warrant a criminal finding of guilt. The jury felt these tax disputes should have been settled in civil proceedings -- as Head's lawyers had argued during the trial.

The jurors were to remain at an impasse -- "hopelessly deadlocked," accoring to a note they gave the judge -- on a third tax-evasion count. Nine or 10 jurors favored a guilty verdict on this charge and two or three held out for acquittal.

In trying to prove this count, prosecutors had asserted that Raven's Hollow fraudelently evaded more than $43,000 in taxes in the firm's 1973 fiscal year. A minority of the jurors believed, however, that there was insufficient evidence that Head had improperly tried to evade taxes.

In reaching that point, the jurorss discussed evidence of tax abuses, focusing, in part, on two key items.

One of these was the prosecution's contention that Head had secretly arranged a carefully "laundered" $11,000 loan to former IRS agent Hare, who had performed an audit of Airlie's tax returns. The loan was allegedly made in return for lenient tax treatment for Head's enterprises.

A second key piece of evidence was a book, turned over to the jury, which outlined standards of ethical conduct required of IRS employess. Relying at least partly on the IRS code of conduct and testimony about the alleged loan to Hare, the jurors concluded that an illegal conspiracy had been formed and that Head was guilty of participating in it.