His motives are clear and understandable. In order to effect a fundamental change in political and social policy, he has to become prime minister. That suits his personal ambitions, too. But in Israel, a person who wants to become prime minister needs a military calling card.

The last elections have shown this again. Peretz wanted to win as a "social" candidate. All the polls proved that he was indeed perceived by the majority of the voters as the most creditable candidate in social matters. But the battle was won by the candidate who was able to dictate the location of the battlefield. Peretz failed to drag social issues to the center of the stage. Olmert succeeded in keeping security there.

The Hamas victory in the Palestinian elections, the continued launching of Qassam rockets from the Gaza Strip into Israel, the Israeli army attack on the Jericho prison, the worsening Iranian nuclear threat - all these pushed the social problems aside. The public was not prepared to vote for a person "without security experience".

In the last 30 years, Israel has had seven prime ministers. Three of them (Yitzhak Rabin, Ehud Barak and Ariel Sharon) were generals. Two (Menachem Begin and Yitzhak Shamir) had outstanding records as chiefs of military underground groups, and Shamir has also served as a senior Mossad officer. One (Shimon Peres) was a former minister of defense and the father of the Israeli atom bomb. Binyamin Netanyahu was only a captain in a commando unit, but he bathed in the reflected glory of his heroic brother, Jonathan, who was killed in the Entebbe raid.

Peretz needs a security certificate in order to prepare himself for the next round of the battle for the Prime Minister's office. That's why he accepted the job of minister of defense, knowing that it could turn into a horror show.

UPON ENTERING the office of the minister of defense, Peretz will have to choose between joining the cannibals or being eaten by them.

In the corridor leading to his new office, there hang the photos of all his predecessors. He would be well advised to pause for a moment's reflection before the portrait of the second in the row: Pinhas Lavon.

Like Peretz, Lavon was a Labor politician lacking any "security experience". In 1953, David Ben-Gurion surprised everybody by appointing him as his successor in the defense ministry. At that time, too, there were some who suspected that it was a trap. Ben-Gurion, who was retiring temporarily to the Negev, turned the job over to the most unsuitable person, so as not to have an effective rival when or if he decided to come back.

Lavon, until then the whitest of doves, turned overnight into a screeching hawk. For example, after soldiers destroyed the furniture of an Arab family while searching their home, he remarked cynically: "They were not of mahogany, were they?" (After that, we in Haolam Hazeh magazine called him "Pinhas Mahogany".) He authorized brutal "retaliation raids" and underwrote the army's determination to sabotage the regime of the new Egyptian leader, Gamal Abd-al-Nasser.

The end was sad. Following this line, the army carried out a false-flag sabotage campaign against US and British targets in Egypt designed to cause strife between Egypt and the West. The action failed, the agents were caught and the army chiefs pointed the finger at Lavon, who had to resign shamefully. (This "affair" had far-reaching political results and led eventually to the downfall of Ben-Gurion himself).

Until now, almost all the defense ministers have been generals. The few exceptions - Levy Eshkol, Shimon Peres and Moshe Arens - took the easy way out. They just gave the generals all they wanted and adopted their outlook. Because of that, they were considered "good defense ministers".

IF PERETZ goes this way, he will be betraying the hopes invested in him.

The army will demand that he authorize "targeted liquidations", enlarge the settlement blocs (even if a few "isolated" settlements will be dismantled), put up more roadblocks and generally make life for the Palestinian population intolerable. After a year, no difference between him and his predecessors will be detectible.

If he wants to live in peace with the generals, he cannot make significant cuts in the bloated military budget, that shark that eats everything it comes across. Without a big cut, there is no chance for the promised social change. But such a cut would lead to the dismissal of thousands of officers and civilian employees, including the well-organized employees of the military industries. Up will go the cry: Peretz is endangering the security of the state, he is exposing us to the Iranian atom bomb, he is to blame for the deaths of terror victims.

In order to be considered a "good defense minister", Peretz must be content with cosmetic budget cuts and disappoint the public that voted for him.

IF HE decides, to the contrary, to confront the generals, significantly cut the military budget and impose on the military a different political outlook, he will find himself a very small David up against a very menacing Goliath.

The Israeli "security establishment" is a power-center that has no parallel in any other democratic state. It includes not only the huge army and all its branches, the big military industries, the Mossad and Shin Bet (which are not even under his control, but report directly to the prime minister). It includes also many hundreds of retired generals, who occupy key positions in all governmental, political and economic spheres, and who can be relied upon to support each other and the General Staff positions.

The Israeli army is not just a professional body. It is also an ideological hothouse. From his induction as a green recruit up to the acquisition of a general's insignia on his shoulders, the officer undergoes an unconscious daily indoctrination which implants in his mind a well-nigh unchangeable outlook. He takes this with him when he moves on, becoming a cabinet minister (whether of Likud or Labor is almost immaterial), the boss of an industrial enterprise or the director-general of an important public service.

This is a political-ideological pressure-machine that no government can hold out against. Ariel Sharon, himself a victorious general, could here and there impose his authority on the military. This does not apply to a government headed by three rank civilians: Ehud Olmert (who has hardly been a soldier at all), Amir Peretz (a junior non-combatant officer) and Tsipi Livni (no military record to speak of) . They will be afraid of being accused by the Chief-of-Staff of not understanding anything about military affairs and endangering the life of soldiers and civilians. All the more so since the army holds the one position that is more important than anyone else, perhaps including the Prime Minister: the army intelligence chief, who bears the sole responsibility for the "national evaluation".

This view of the world submitted to the cabinet by Army Intelligence practically dictates all its political and security decisions. No minister will ever stand up and say: "Dear comrades, this is a heap of rubbish!" Not even after it was disclosed that one of the last army intelligence chiefs had systematically falsified the professional findings of his subordinates and submitted to the cabinet a deliberately false picture of Palestinian intentions.

The senior officers corps, by its very nature, looks at Israel's problems through gunsights - that is to say, with one eye closed.

POSSIBLY, PERETZ will change the situation. Possible he will show himself to be a fearless fighter - imposing on the senior officers a political outlook that is alien to them, cutting the fat military budget and insisting on moral standards. Hopefully.

There are military experts who say that if Peretz tries to impose his perceptions, the Chief-of-Staff and his generals will eat him for breakfast. Peretz' admirers believe that it will be he who leaves that cannibal meal with a full stomach.

It is said that a clever person knows how to get out of a trap that a wise person would not have walked into in the first place. But when a person enters a trap with open eyes, one can only hope that he knows how to get out - and at least keep one's fingers crossed for him.