ONCE again Israel's ``national unity'' government teeters on the brink of extinction. Once again it will likely be saved by the grace of Shimon Peres. Once again the beneficiary will be Yitzhak Shamir, whose Likud Party ought by now to have reserved a permanent place on its honor roll for Labor's Mr. Peres. The issue this time is Shin Beth's cover-up of an incident in which suspected terrorists were said to have been clubbed to death in Shin Beth custody.
Mr. Shamir and Likud oppose any inquiry, but will accept one with sharply limited jurisdiction. Peres, no more enthusiastic than Shamir, has been pushed by several of his Labor colleagues and constituents into grudging acceptance of an inquiry.
Since the Likud could, along with its religious-party allies, block any Cabinet move for an investigatory body with teeth, the option favored by an apparent Labor majority is for Peres to treat an adverse vote as one of no confidence and seek new general elections.
But Peres is far more inclined to seek a solution the Likud can live with -- perhaps a nonjudicial body armed with a silent mandate to bury vague findings under an avalanche of praise for Shin Beth and dicta about the need to put the nation's security first.
Shamir's situation is clear. A founding member of the pre-statehood Stern gang, a longtime Mossad secret service agent, and a right-wing politician who, according to court documents and other published reports, approved the cover-up in the current case, he has little to gain from an inquiry save carefree retirement.
Peres's position is more complex.
To review, the episode began with an April 12, 1984, bus hijacking near the city of Ashkelon. Of the four Arab terrorists involved, two were killed when Israeli forces stormed the bus and the other two taken into custody.
After interrogation by Army Gen. Yitzhak Mordecai, the two prisoners were turned over to Shin Beth, Israel's internal-security agency which operates primarily in the occupied territories and Arab communities inside Israel.
Published reports indicate that while the men were in his custody, Shin Beth director Avrum Shalom allowed them to be clubbed to death.
There followed an obstruction of justice in which the Shin Beth chief and his agents lied about their roles to the minister of defense and at least two specially commissioned investigations.
General Mordecai, ultimately acquitted, was left to confront a military investigation that lasted more than a year, a situation the dean of Tel Aviv University law school called ``an internal Dreyfus affair.''
Shin Beth officials who objected to the cover-up were mercilessly driven out of the service, their careers wrecked by Mr. Shalom.
Peres became prime minister in September 1984, while the cover-up was in full swing. He told the Knesset that in October 1985 he was warned by Shin Beth's then deputy director, Reuven Hazak, that the entire affair ``smelled rotten.''
In reply, Peres expressed fury over being approached nearly 18 months after the hijacking and full confidence in Mr. Shalom, and he suggested that perhaps Mr. Hazak should leave Shin Beth.
Disenchanted Shin Beth officials finally took the matter to Attorney General Yitzhak Zamir, who found a police investigation warranted. Peres fought Mr. Zamir tooth and nail, helping finally to ease him out of government.
In a remark that received far too little attention here, Peres told the Knesset he feared a police inquiry because the defense to criminal charges by Shin Beth officials -- precedent -- would have exposed other secret operations. One wonders, precedent for what? Murdering prisoners? Lying to the Cabinet? Obstructing justice?
In any event, Zamir's successor, Yosef Harish, also urged a criminal or judicial commission inquiry.
To short-circuit this route, Shalom approached President Chaim Herzog offering to trade his resignation for a full pardon for himself and his top three culpable aides. Mr. Herzog agreed, provided the inner Cabinet approved the arrangement. Peres led his colleagues, save Ezer Weizman, in joining a unanimous Likud contingent behind the deal.
But by now top Labor officials, prominent lawyers, and much of the political left were up in arms. They demanded some adherence to the rule of law, even where an agency like Shin Beth, which performs a vital antiterrorism role, is involved.
They urged a judicial commission of inquiry of the sort that had investigated the massacre at the Sabra and Shatila refugee camps, one empowered to find facts and make recommendations even while protecting legitimate security interests. And they wanted to know why Peres had once again placed his rotation agreement with Shamir above the apparent best interests of his party and his society.
Among Mr. Peres's colleagues, a variety of explanations are offered. Some say he knows that the sentiment of the Israeli elite notwithstanding, Shamir and company would do well campaigning as the defenders of the nation's antiterrorism watchdog. Some hold Peres as being so anxious to live down his ``tricky'' image that he will in no case jeopardize October's planned rotation.
Others see in the prime minister an inner weakness and indecisiveness for which even his high intellect cannot compensate.
Finally, many see Peres a creature of his own lengthy background in national-security areas. In this view, despite the yawning ideological gulf between them, when Peres and Shamir talk about Shin Beth, it is just one ``old boy'' to another.
C. Robert Zelnick is chief correspondent for ABC News in Tel Aviv.