Many people find Menachem Begin obnoxious. But in the case of the Israeli prime minister it is a mistake to identify personality with policy.

Indeed, largely because of his unattractive qualities, Begin has been far more forthcoming in negotiation than any other Israeli leader could have been. If he nearly always says the wrong thing, he nearly always does the right thing.

The indictment of Begin as an individual fairly bulges with charges. He haggles like a shyster, lectures like a magistrate and is touchier than a dispossessed nobleman. He talks to the point of making Howard Cosell seem a "mute, inglorious Milton."

He wears his Zionist faith on his sleeve, and constantly rubs it in other people's faces. He has a "Holocaust complex," and identifies disagreement with what the Germans did to the Jews.

Instances galore back up these charges. The Camp David summit was barely over before Begin was into a legalistic quibble as to whether Israel was obliged to cease building new settlements on the West Bank of the Jordan River for a period of more than three months. In briefing after briefing he explained why the West Bank ought to be called by its biblical names, Judea and Samaria.

His speech at the White House signing ceremony should have been cut in half. Particularly unnecessary was a Hebrew section hardly anybody present could understand. Within days of the Camp David summit, Begin was boasting to the world of his glorious achievements.

But all these tasteless actions only show Begin thorough a glass darkly. To see him whole requires a look at concrete negotiating matters.

The current fuss over the West Bank settlements presents a nice case in point. No settlements are planned for the next three months. Before three months are out, there is supposed to be a Palestinian authority on the West Bank. Such an authority would never grant persission for a Jewish settlement.

Even if the authority does not materialized, the Israel would not risk a break with the United States - and the peace with Egypt - by building further settlements. So at worst Begin will continue to yell his head off white doing nothing.

The happy contrast between words and deeds finds support at every step of the way to Camp David. Whenever there was a concrete issue for negotiation, Begin compromised.

The first step came on Sept. 17, 1977, when Foreign Minister Moshe Dayan met in Morocco with Hassan Tuhami, an Egyptian diplomat, to arrange a possible visit to Israel by Sadat. At that point, Begin was prevailed upon to promise that if such a visit took place he would abandon all claims to sovereignty over the Sinai Desert - the basic element of the Camp David accord.

A second step took place on Oct. 5, 1977, when Dayan produced with Secretary of State Cyrus Vance a joint Israeli-American working paper. The United States came off previous insistance that a place for the Palestine Liberation Organization be made at the peace table. In return Begin accepted a formula later picked up in the Camp David talks, and wrongly identified by some as a crucial breakthrough - namely, that the future of the West Bank be settled through negotiations among Israelis, Jordanians and Palestine Arabs.

A third step took place at the Ismailia summit meeting with Sadat in December 1977. To engage the Egyptians furhter, Begin abandoned the previous insistence of all part Israeli leaders that there had to be a splitting of West Bank territory between Israel and the Arabs.

A fourth step took place at the meeting of Israeli and Egyptian foreign ministers in England in July. At that point Begin agreed that the issue of sovereignty over the West Bank could be negotiated before the end of a transition period.

These successive concessions paved the road to Camp David. Without them no agreement would have been possible, and in each case concrete negotiation yielded concession on Begin's part that was not forthcoming when the issue was a matter of buzz words or abstract principles.

The ultimate proof that Begin is unyielding in talk but accommodating in action is Camp David itself. For what did Jimmy Carter basically do at the summit? He took the pressure off the Israelis. With the bristles thus out of the Begin personality, Israeli officials were able to draw from the prime minister the concessions always implict in his policy.