Four of the federal court jurors who decided last week that The Washington Post libeled Mobil Oil Corp. president William P. Tavoulareas in a 1979 article initially supported the newspaper, but acceded to the position of the two other jurors in order to avoid a hung jury.

In the end, the critical factor in the jury's decision, according to three jurors interviewed this week, was the fact that the key source for the article on Tavoulareas' business dealings, shipping executive George Comnas, was not called as a witness by The Post's attorneys.

One juror, who described herself as the last holdout before the jury decided in favor of Tavoulareas, said she agreed to the verdict because "the pressure was getting to me. I started having palpitations.

"I don't know what happened to me," the juror said. "I think it was a wrong decision, a total wrong decision. It's been worrying me and worrying me.

"Really . . . it should have been" a hung jury, the woman said, declining to be identified by name.

The jury, after deliberating 18 1/2 hours over three days, found that the Nov. 30, 1979, article by reporter Patrick Tyler libeled the Mobil president and awarded him $2,050,000 in compensatory and punitive damages. The article detailed the 1974 creation of Atlas Maritime Co., a London-based shipping management firm in which Tavoulareas' son, Peter, was a partner and described how the company did business with the Saudi Maritime Co., a shipping firm in which Mobil is a partner.

The younger Tavoulareas also was a plaintiff in the case, but the jury cleared The Post of the libel charges he brought. In a companion case, the jury found that Dr. Philip Piro, an eye surgeon and former son-in-law of Tavoulareas' who was an early source for the story, had slandered both Tavoulareases and awarded the Mobil president $5,000 and his son $1,000.

E. Franklin Johnson, a 56-year-old Commerce Department oceanographer, and two other jurors who declined to be identified, said they believed the basic accuracy of the story. But they said they were unable to cite specific evidence supporting their position to the two jurors who did not believe the elder Tavoulareas was involved in the establishment of his son in the London business.

"You cannot persuade a person to go against his will," Johnson said in an interview. "They the two against The Post from the start said, 'Go through the 160 documents submitted as evidence and show me where William set up Peter.' They asked me for concrete proof. I could not find one piece."

The two jurors who favored Tavoulareas' libel claim from the start were jury foreman Geoffrey T. Mott, a 27-year-old librarian at the Library of Congress, and David A. Ford, a 32-year-old Western Electric Co. storekeeper, according to one of the jurors who was interviewed. Both Mott and Ford declined to be interviewed.

Johnson said The Post's sometimes flamboyant attorney, Irving Younger, was "a wonder to watch, but why he didn't put George Comnas on the stand, I'll never know. He was his key witness. I was shocked out my tree that Younger did not put George Comnas on the stand.

"I didn't want the compromise," Johnson said. "We did compromise. The fact that George Comnas wasn't on the stand . . . . It didn't make me compromise, but it surely did lead me that way.

"It was just a matter of having to come back with a verdict," he said. "Either you do that or have a hung jury. It would have been unfair to have a hung jury."

He said the fact that $2 million was awarded, "that alone tells you it was a big compromise compared to $50 million" that the Tavoulareases had sought. He said one juror had wanted to award William Tavoulareas a dollar, while another thought $1 million was appropriate for compensatory damages. They compromised on $250,000 and later assessed $1.8 million in punitive damages against The Washington Post Co., which was the amount of the elder Tavoulareas' legal fees.

Tyler testified that Comnas "was an important source for this story." Neither side called Comnas as a witness, although an extensive pretrial deposition had been taken from him. Younger declined comment yesterday and would not say why he did not call Comnas.

The juror who described herself as the last holdout said the absence of Comnas did not bother her. But she suggested that the impact of the large number of documents in the case, some of them technical in nature, was lost on the jury.

Nonetheless, she said one juror, whom she declined to name, viewed a memo written by Post copy editor Cass Peterson before the article was published "as the truth." Peterson wrote that after reading the Tyler story several times, she was "still left with an overwhelming sense of So What? . . . It's impossible to believe that Tavoulareas alone could put together such a scheme for the sake of his son's business career, or that he would want to."

In his instructions to the jury, U.S. District Judge Oliver Gasch said the criterion for deciding whether Tavoulareas had been libeled was whether the jurors believed the story to be false and defamatory and whether The Post knew it to be false when it was published or demonstrated a "reckless disregard" about the accuracy of the article.

Lawyers for The Post have asked Gasch to set aside the verdict, or alternatively to order a new trial or reduce the amount of the damages. Lawyers for the Tavoulareases have asked for a verdict in favor of the younger Tavoulareas or a new trial for him and larger damage awards for both. Gasch is not expected to rule on the requests until later this year.