Only a glimmer of fundamental changes in Israeli psychology wrought by Prime Minister Menahem Begin is visible today, but the boldness of that change shows that, if his health holds up. Israel will be far more formidable on the world stage than even before.

Following 30 years of rule by the Labor coalition, flabby and scandal-ridden when it lost the election last May. Begin shows none of the self-conscious reserve of a Levi Eshkol or a Yitzhak Rabin, two of Labor's prime ministers. Israel's new mood, a flattering and revealing reflection of Begin himself, is one of uninhibited militancy about Israel's place in the sun.

For the first time since Israel conquered East Jerusalem from Jordan, an American official was snubbed by Jersalem Mayor Teddy Kollek, and the snub made headlines. The issue was Treasury Secretary W. Michael Blumenthal's routine request to Kollek for an "official" tour of West Jerusalem, but not East Jerusalem. The United States does not recognize Israeli sovereignty over former Jordanian territories.

Although every U.S. official has handled this political problem the same way, Kollek refused to play host for Blumenthal. Kollek claimed he needed no U.S. approval for the unification of Jerusalem: "The city was already unified, by King David."

The rebuke was symbolic of Begin's milnant, didactic politics of psychology. In Washington last summer to meet President Carter, Begin was briefed by aides on questions he would be asked on "Meet the Press." He answered the first rehearsal question with an evocative recital of the fall of the second temple in Tisha Bav, the ninth month in the Hebrew calendar, A.D. 70. He told his surprised briefers: Whatever the first question I am asked, this will be my answer.

Begin is an ardent believer in the mystical link that connects modern Israel with the Kingdom of David and, later, the cataclysm of Bar-Kochba, the doomed Jewish revolt against Rome in the year 130 that ended in slaughter of the Jewish remnant.

"The world does not pity the slaughtered," Begin wrote in "The Revolt," his brilliant, chilling description of his terror campaign against British control of Palestine," it only respects those who fight."

He has created a mood of excitement and purpose that revolves around himself and has infected many of his people (but dismayed and frightened some). He commands the strongest Knesset majority ever, having outfoxed the new Democratic Movement for Change, which joined his Likud coalition two weeks ago on humbling terms.

In sharp contrast to previous governments, Begin totally dominates the issues he believes important: defense, foreign policy and, most important of all, relations with the United States. Elsewhere, he dislikes interfering with his generally undistinguished ministers, although, of course, such major (and politically risky) decisions as devaluation of the pound and the cut in consumer subsidies were made in the prime minister's office.

The change in the Knesset is equally dramatic. Begin insists on attending all sessions of the parliament - shunned by his predecessors as time-consuming and boring. Naturally, his ministers do the same. So far, he has left the civil service virtually untouched, despite fears of wholesale housecleaning.

Likewise, factional politics and playing favorites seem beneath Begin. When one very important Israeli ambassador started cutting corners around Foreign Minister Moshe Dayan for private communication with Begin, Dayan "with the express knowledge of the prime minister" ordered him to stop.

One Begin problem dwarfs all others: the U.S. connection. Significantly, Moshe Arens, a Begin ally and fourthranking member of Begin's Herut Party, warned in the Jerusalem Post 10 days ago that Israel "is just at the start of a long dispute [with the U.S.], a contest for public opinion . . . We must decide on what issues we can buy the impression of flexibility and on what others we must draw the red line." That exactly reflects Begin's political strategy in his battle for the U.S. Congress.

In "The Revolt," Begin extolls "the fighting Jew . . . a specimen completely unknown to the world for over 1800 years." He wants American Jews to become "fighting Jews" for Israel in the political battle ahead. If Begin's charismatic leadership here is an indicator, President Carter will need every weapon and every strategem he can lay his overburdened hands on to prevail.