Of the issues before the jury in Ariel Sharon's libel case here, the question of whether Time magazine acted with "actual malice" in describing the former Israeli defense minister's role in the 1982 Beirut massacre is proving to be the most time-consuming and difficult.

Today, the six-member federal jury made its fourth request for a large portion of the trial's testimony and exhibits since it began late Friday to weigh the often-confusing testimony against Judge Abraham D. Sofaer's extremely complex instructions. They retired this evening without deciding the issue.

The legal concept of "actual malice" has been the major stumbling block for other juries in libel suits brought by public figures. Jurors' misinterpretation of what it means has been the reason most frequently cited by appellate courts in overturning jury libel verdicts.

Broadly speaking, "actual malice" requires a finding that a defendant who published or broadcast false and defamatory information knew that it was false or had reason to doubt that it was true. But beyond that, the concept is murky.

On several occasions during the trial, and again in his 20 pages of written instructions on "actual malice," Sofaer has reminded jurors that the courts do not penalize the news media for mere bias, hatred, negligence, sloppiness or even error -- or the countless other conventional meanings the non-lawyer might draw from the term "malice."

Upstairs in the federal courthouse here, U.S. District Court Judge Pierre N. Leval has told lawyers in retired general William C. Westmoreland's libel suit against CBS Inc. not to use the term "actual malice." He prefers to discuss the concept by referring to the "state of mind" of CBS employes who put together the documentary at issue in that trial.

Even First Amendment lawyers say that the term "actual malice" was ill-chosen by the Warren Supreme Court when, in the landmark Sullivan v. New York Times case, it attempted to set some outer limit on the news media while, at the same time, broadly interpreting freedom of speech as it applies to media reports and comment about public figures.

In Sullivan, the Supreme Court spoke of "a profound national commitment to the principle that debate on public issues should be uninhibited, robust and wide open and that it may well include vehement, caustic and sometimes unpleasantly sharp attacks on government and public officials . . . . "

" . . . Erroneous statement is inevitable in free debate," the court said, "and . . . must be protected if the freedoms of expression are to have 'breathing space' that they need to survive."

But the courts consistently have refused to grant the media free rein in writing about public figures. In the Sharon case, Sofaer rejected Time's argument that the press should enjoy blanket immunity against libel when writing about figures like Sharon and their conduct of such weighty matters as war because such officials enjoy an immense stature and power and can command public attention to rebut allegations if falsely defamed.

But Sofaer responded, "Nothing in the First Amendment requires that the press have absolute freedom to pass off . . . rumors as fact, regardless how certain a reporter is of their falsity or how damaging they are to an official's reputation.

"The Supreme Court has rested its denial of absolute immunity on the fundamental premise that the constitutional value of free speech does not in all circumstances outweigh the state's interests in protecting the reputations of their citizens."

Perhaps the classic example of the kind of outrageous media behavior the courts have declined to protect was illustrated in the suit of Sen. Barry Goldwater (R-Ariz.) against maverick publisher Ralph Ginzburg for a 1964 article in Ginzburg's now-defunct Fact magazine. Purporting to be a psychobiography based on a poll of psychiatrists, a Fact article concluded that the 1964 Republican presidential nominee was suffering from a serious mental disease.

The court found that Ginzburg, starting from a "predetermined and preconceived plan to malign" Goldwater's character, had edited and tampered with the psychiatrists' responses -- "melding and distilling" was Ginzburg's way of describing his methods -- in a calculated effort to fabricate information making Goldwater look bad.

Another case that helped define curbs on the media's freedom was entertainer Carol Burnett's successful suit against the National Enquirer for writing that the actress was tipsy one night at a Georgetown restaurant and had an argument with Henry A. Kissinger.

Burnett's lawyers, in the rummaging, pre-trial discovery process, made a couple of surprising finds in the Enquirer's files. Contrary to suspicion about how it goes about its reporting, the tabloid seemed to have done a pretty careful job of checking leads on Burnett -- amassing considerable details to indicate that what the tabloid eventually printed was, in fact, wrong. During the trial, nobody at the Enquirer could explain why the item had been published.

The Supreme Court also has indicated that the press might not enjoy protection against libel where published information that is defamatory and false is based on an unverified anonymous telephone call or is so improbable that only a reckless reporter would write it and in cases where there are obvious reasons to doubt the veracity of the sources of an article.

In the Sharon case, however, Sofaer has plunged into what one libel warrior called a "dicey area" by instructing the jury that it could find against Time if it decided that the magazine had "so exaggerated or distorted" information they received to the point they were aware it was "probably untrue."

Sofaer provided the panel with a kind of road map for sorting through evidence to decide whether Time acted with "actual malice."

"Some judges shy away from that kind of thing," said Henry R. Kaufman, general counsel for the Libel Defense Resource Center, a New York-based media group, "because they think it's too subjective and it's difficult, if not impossible to do without putting your thumb on the scale one way or another."

Other lawyers point out that the concept of actual malice is, in many cases, ultimately a subjective judgment.