The conventional wisdom has been that the American people would (and should) forgive President Clinton even if Kenneth Starr can prove that Clinton lied about sex, assuming that’s all Starr can prove.

I share that view, at least in terms of legal consequences, because perjury in a civil deposition to hide a private, consensual affair that is of tenuous relevance to the lawsuit at hand falls on the low end of the culpability scale, as felonies go.

But what if the president were to go before Starr’s video camera on Aug. 17 and repeat–in the crucible of criminal investigation–his earlier sworn denial that he had any kind of sexual relations with Monica Lewinsky? And his sworn denial that he had ever met alone with her other than on routine business? And his sworn denial that he had discussed with her how she might dodge her subpoena to hand over any gifts she had received from Clinton and to testify truthfully in the Paula Jones case? And what if Starr can prove all of those statements, and more, to be lies?

Would, or should, the public forgive Clinton that?

I don’t think so. I think that the verdict would be swift, sure, and severe, partly because perjury is especially serious when it comes in a criminal investigation, and partly because people would understand that Clinton had very deliberately chosen to spurn another, more honorable option.

That’s the option of coming clean. Clinton could publicly admit that he lied in January–to protect the privacy of Lewinsky, his family and himself–and he could ask the public to pardon him for this.

Although the president’s advisers are saying that he has no intention of changing his story, the come-clean option remains open, at least until Aug. 17. It is one of four possible courses that were presented by the confluence of Starr’s subpoena demanding Clinton’s testimony and Starr’s immunity deal with Monica Lewinsky.

The three other options were for Clinton 1) to fight Starr’s subpoena in court on the ground that it violates the Constitution’s separation of powers; 2) to become the first president in history to take the Fifth; and 3) to repeat and embellish, in testimony to be videotaped for Starr’s grand jury, his detailed Jan. 17 deposition testimony and his forceful Jan. 26 vow to the nation that he had neither had sexual relations with Lewinsky nor told anybody to lie.

Option 1 must have had some appeal to Clinton’s lawyers. Although it would be a long shot in court, it could have purchased precious weeks or months. But fighting the subpoena would have had a high political cost, spreading dismay among Democrats in Congress. So that option was effectively abandoned this week, when Clinton agreed to testify on Aug. 17. Option 2, which may be even more politically unpalatable, seems not to be under consideration.

By all signs, the president is heading toward Option 3, the brazen-it-out strategy. But this choice presents a danger of the gravest kind. It could effectively end the Clinton presidency, if Starr can prove that the president–who undertook a constitutional duty to ”take care that the laws be faithfully executed”– has not only lied in the past but is lying still, in a cynical effort to thwart a criminal investigation.

This analysis rests on two assumptions that may or may not prove out: That Starr will be able to prove that Clinton has lied so far about his dealings with Lewinsky, but may not be able to implicate Clinton in a conspiracy to enlist others (like Linda Tripp and Clinton’s secretary Betty Currie) in a broader coverup. While it would be pure conjecture to bet for or against the second assumption, I would put my money on the first.

Defenders of the president–few of whom believe that Clinton has told the truth about Lewinsky–nonetheless express confidence that Starr cannot prove that Clinton has lied, even if Lewinsky so testifies: It’s a ”he-said, she-said” standoff, Clinton defenders keep prattling, and he cannot be proved a liar just because she says he’s one. It’s true that Monica Lewinsky will never be a very credible witness, and that her testimony alone could not prove by any reasonable measure that Clinton had sex with her, or lied to cover it up, or encouraged her to do so.

But what Clinton defenders prefer to ignore is the apparently massive body of corroborative detail that Starr has spent the past six months pulling together, in the face of angry attacks for overzealousness by the same folks who are now preparing to trash him for giving credence to so flawed a witness as Lewinsky: The so-called ”sting tape” that Starr’s agents made by wiring Tripp for a four-hour meeting with Lewinsky on Jan. 13, the bookstore records that Starr subpoenaed to corroborate Lewinsky’s taped account that she had given Clinton certain books at certain times, the Secret Service testimony that the administration strove so mightily to prevent, and more.

First, of course, there are the 20 hours of Tripp- Lewinsky tapes–described by one person who has heard them as ”jaw-dropping” in their probative force–and Tripp’s detailed handwritten notes of other conversations. The tapes and notes contain dozens of contemporaneously recorded dates, times, places and other specifics so vivid that those who have heard and seen them will have a very hard time believing any claims by Clinton that Lewinsky was fabricating or fantasizing.

It will be even harder to dismiss the tapes once they have been corroborated–day-by-day, hour-by-hour–by White House logs showing that Lewinsky was visiting on the relevant dates and times; by Secret Service sightings of her going to see Clinton alone; by the recollections of White House aides and others; by gaps in the president’s official schedule; by phone records; by the gifts–including a brooch and a hat pin–that Clinton gave Lewinsky and that later, while under subpoena, she transferred to Betty Currie.

The president will be questioned in painstaking detail, by prosecutors skilled in the art of cross-examining smart, slippery witnesses, not only about the big issues–such as whether he had sex with Lewinsky and encouraged her to lie–but about the dozens of details that shed light on those larger questions. Not even a man as quick-witted and rhetorically gifted as Clinton can safely lie his or her way through such a session without running a grave risk of being caught in a net of irrefutable proof.

Such proof would either end Clinton’s presidency or reduce him to grimly hanging on until Jan. 20, 2001, ruined as a leader and facing disgrace in hist ory’s judgment. The come-clean option might save Clinton from both fates–if he can credibly deny orchestrating a larger cover-up.

If Clinton does plan to stick by his story, his lawyers should first fill him in on what happened to another man who stuck by his story, in the face of another alleged right-wing political vendetta.

That was Alger Hiss. His ill-fated federal grand jury testimony came 50 years ago. Hiss was subsequently convicted and imprisoned not for being a Communist spy–a crime on which the statute of limitations had run out–but rather for two counts of perjury. Hiss had sworn 1) that he had never given copies of State Department documents to Whittaker Chambers, a self- described former Communist underground organizer, and 2) that he had never seen Chambers after Jan. 1, 1937.

The main prosecution witness was the far-from- unassailable Chambers. He was trashed by Hiss’s lawyer as a ”moral leper.” His credibility and persona were widely derided by the sleek, slick Hiss’s defenders–just as Linda Tripp is derided now.

But Chambers was able to recall his alleged dealings with Hiss, and such things as the layouts of Hiss’s homes and furnishings, at a level of detail that–if less vivid than the dozens of Lewinsky narratives captured on Tripp’s tapes–was copious enough to impress both the jury and the federal appeals court that affirmed Hiss’s convictions.

Chambers was also corroborated (the court stressed) by evidence that copies of 42 sensitive State Department documents, which Chambers had said he had been given by Hiss, had been typed on a Woodstock typewriter owned by Hiss and his wife. The court also noted the sheer implausibility of Hiss’s efforts to explain away such telling evidence as the product of a conspiracy against him.

Starr may not have anything quite like that Woodstock typewriter to nail down a perjury rap against Clinton. But he does have Lewinsky, and Tripp, and the tapes, and much, much more.

Clinton, for his part, has one last chance to tell the truth.