''In style, a big difference; in policy, basically the same.'' This is the way that one well-informed Israeli summed up the change that newly appointed Defense Minister Moshe Arens, currently Israel's ambassador to the United States, will bring to Israeli defense policy when he replaces the controversial Ariel Sharon.
US policymakers will be particularly interested in this difference since they have recently tended to attribute deteriorating relations with Israel largely to Mr. Sharon's style, tactics, and hard-line views.
The Israeli Cabinet voted to take Mr. Sharon's portfolio away from him after he was severely criticized by the Kahan Commission inquiry into the massacre of Palestinian refugees in Beirut by Christian Phalangist militiamen.
Mr. Sharon refused to resign and rejected the commission's attribution of indirect responsibility to Israeli officials. He will remain in the government as minister without portfolio. His future responsibilities remain unclear, though he has let it be known, via his spokesman, that he does not consider himself ''defeated'' and has not abandoned hopes of one day becoming prime minister.
Prime Minister Menachem Begin's choice of defense minister may be seen as a signal that nothing has changed in Israeli policy despite the political upheavals of the past week.
Mr. Arens is considered one of the most hawkish leaders of the Herut Party, Mr. Begin's wing of the governing Likud coalition. He is not expected to be ''softer'' on key issues than was Mr. Sharon. He told an Israeli interviewer that he ''unstintingly supports the policies of Prime Minister Begin and the government.''
Mr. Arens had, in fact, been offered the defense portfolio in 1980 when Ezer Weizman, then defense minister, resigned. But he refused it because he opposed the terms of the peace treaty with Egypt. He believed that Israel should have retained its two giant air bases in the Sinai and that Jewish settlers there should have been allowed to stay.
Nonetheless, Israeli observers accept that Mr. Arens's style - more personable and diplomatic than the abrasive Mr. Sharon - is likely to ease tensions between Israel and the US. This is all the more true since personalities have come to play such an important role in setting the tone of the US-Israel relationship.
While Mr. Arens may still be a ''maximalist'' in terms of protecting Israeli interests, says Jerusalem Post military correspondent Hirsch Goodman, ''He won't use the same all-or-nothing tactics as Sharon.''
In practical terms this means, says Mr. Goodman, that Moshe Arens will make ''a much more detailed and realistic assessment of what Israel can achieve and use this as a guideline. Arens will look more at the broader picture than Sharon ever did.''
This could mean in negotiations on Israeli troop withdrawal from Lebanon that Israel would be more flexible on specific points so long as Israel's overall security interests are protected. On the other hand, Mr. Arens is said to believe that some Israeli troops should stay in Lebanon to man anti-terrorist posts, and he has publicly criticized the United States in the past for pressuring Israel to withdraw from Lebanon in the absence of a formal peace treaty.
It could also mean that the Israeli Foreign Ministry's viewpoint, which tended toward such flexibility but was ignored by Mr. Sharon, may get more attention.
On the West Bank issue, observers note that Mr. Arens sent Mr. Begin a controversial memo last year containing the option of a temporary settlement freeze as a way of improving US-Israeli relations. He is, however, fully supportive of Israeli government policy on settlement and on ultimate retention of the occupied Arab territory.
From the US perspective, Mr. Arens's extensive familiarity with America will be a plus. Born in Lithuania, he was brought to the US at age 13 in 1938. He subsequently returned to the US to study aeronautical engineering at both the Massachusetts and California Institutes of Technology after fighting in Israel's 1948 war of independence.
After working in the US aircraft industry, he returned to Israel where he became the vice-president for engineering at the Israel Aircraft Industries. After entering politics, he became chairman of the Knesset (parliament) foreign affairs and defense committee.
As Israel's ambassador to the United States he has developed extensive contacts with pro-Israel US congressional leaders and American Jewish community spokesmen, which, say observers here, has made him sensitive to US concerns.
Prime Minister Begin, who is holding the defense post temporarily, moved more quickly than was expected on the Arens appointment in order to assure continuity on defense policy at a time when Israel has a heavy military commitment in Lebanon. The Israeli military establishment has been shaken by the Kahan Commission's criticism of senior officers, including retiring Chief of Staff Rafael Eitan.