The ghost at Prime Minister Yitzhak Rabin's shoulder as he accepted his party's hair-thin vote of confidence early this morning was the new spirit of political reform engendered by Israel's world famous scholar-soldier, Yigael Yadin.

When the professor, former chief of staff and archeologist firs threw his hat in the political arena only three months ago, most observers thought him an attractive amateur whose new party might at best win two or three of Parliament's 120 seats in the May election.

Today Yadin's Democratic Movement for change has become the refuge for a host of Israelis who are disillusioned with old-style party politics.

Pundits say that he could capture between 15 and 22 seats in the elections. This would not be enough to outpoll either Rabin's ruling Labor Party or, probably, the major opposition party, the Likud. But it might be enough to make Yadin the indispensable coalition partner for Rabin or anyone else trying to form a government.

Dissatisfaction with old political customs and scandals has become endemic in Israel. Hardly a week goes by without some well-known public figure announcing that he has quit his former party and is throwing in with Yadin.

It was clear from speeches and deliberations during the Labor Party convention yesterday that Yadin has already had an influence on the party that has ruled Israel since independence in 1948. Largely because of Yadin's movement, Labor candidates must stress their willingness and ability to bring about change and reform.

Bothe the Labor and Likud parties are now talking about opening up the smoke-filled committee rooms to make the selection of candidates more open. Yadin's own party plans to hold primaries in March in which all party members can elect their candidates for the May general election. This will be the first time in Israel that such a primary has been held.

Although Labor is expected to win a plurality at the polls in May, the Democratic Movement for Change has been steadily eating into Labor's support.

Yadin said in an interview that he saw a coalition with Labor rather than with Likud as the most likely outcome of the May elections. He said he intends to ask any coalition partner to accept his principles.

His intention, he said, is to use the system to reform it. He would insist, as a condition of his partnership, that the next government of Israel completely reform the electoral process and hold elections under a new system within "a reasonable amount of time - say 12 to 18 months." He would also revise the bureaucracy to make it more responsive to the people.

At present Israelis vote for a party slate - a list of candidates that are chosen in closed meetings for committees.

Voters must vote for the whole party slate rather than for individual candidates. This is one of the reasons Yadin calls Israel the "most undemocratic of the democratic states." He would institute a system of constituencies where people in a given area would vote for a candidate to represent their interests, as in Britain.

Yadin's position on Israeli foreign policy, the occupied territories and national security is not unlike that of the Labor Party's platform and, because his movement has attracted such a wide selection of both hawks and doves, a Yadin victory at the polls would probably not measurably change Israel's foreign policy toward the Arabs.

It is not, however, the specifies that attract people to the Yadin movement. It is their perception of Yadin's honesty, idealism and commitment to change. Not unlike Jimmy Carter, Yadin plays the role of Mr. Outside, uncontaminated by politics and what might be called "the mess in Jerusalem."

Yadin's detractors call him politically naive and they say that the purity of his movement has been polluted and obscured as the number of establishement-type converts has grown.

"I am not sure I want to be purified by ex-intelligence chiefs, policemen and itinerant politicians," said Labor's acid-tongued Abba Eban, refering to Yadin's movement. But Eban acknowledged that a lack of political focus has not stopped the Yadin movement from becoming "the bucket placed under the leaking roof." Eban said that Yadin was "going to catch water simply by standing there no matter what he believes."

With country suffering 30 per cent inflation, constant labor unrest and economic stagnation, and with the Labor Party ridden with scandal, the hole in the establishment's roof ever widens and Yadin's bucket continues to fill.

The bald, pipe-smoking Yadin, 59, often as not dressed in a turtleneck sweater and British-cut tweed jacket, peers at his audiences above his half-lense glasses like a stage schoolmaster. It is hard to imagine that he was a general at 32 and, as chief of staff, laid the foundations for Israel's modern army based on a combination of professionals, a people's army of reservists on instant call and paramilitary settlers on the frontier.

Yadin's father was an archeologist and it was he was bought the first Dead Sea Scrolls from a Bedouin who had found them in a cave. It is said that Yadin used his knowledge of Biblical history during the war of independence to chart old routes across the Negev Desert for his troops.

In 1952 Yadin left the army to devote his life to archeology and in the intervening years he has led the famous digs that uncovered Megiddo, Hazur and Masada - the place where the Jewish zealots of the 1st century committed mass suicide rather than become Roman captives. Yadin has also written extensively on the Dead Sea Scrolls.

Today, Yadin has taken up a third career in politics and no matter how his new movement fares at the polls in May, the Democratic Movement for Change has already defied predictions and turned Israel's political establishment on its ear.