The defense ministers of Isreal and Egypt said today that long difficult negotations lie ahead of the joint military committee but the gap between what Isreal wants and what Egypt can give is bridgeable.

The exchange between Ezer Weizman of Isreal and Gen. Mohammed Gamassi of Egypt as they sat together in the shade of a sycamore tree talking to reporters marked another of the psychological breakthroughs that have transformed the astmosphere of the Middle East since President Anwar Sadat's journey to Jerusalen in November.

Weizman and Gamassi talked to newsman after the 3 1/2 hour session of the joint military committee. During today's round the Israeli side outlined its position on why and where Israel considers itself vulnerable and what kind of protection it wants as part of a peace agreement.

By listening courteously to the Israeli presentation and responding with counterproposals, Egypt has for the first time shown itself ready to take Israel's security concerns seriously, to accept them as genuine instead of dismissing them as a cover for Zionist territorial ambitions.

The ritual Egyptian response to Israeli expressions of concern about security - that they are trumped up to give Israel an excuse to keep the territories occupied in the 1967 Arab-Israeli war - was not to be heard today after meeting in which Israel's chief of staff, Gen. Mordechai Gur, made what Gamassi called "a presentation of Israel's security problem."

Weizman said that 'what Gur presented this morning was received in the genuine way that it was delivered . Obviously there are things that are not accepted and things to be discussed. This is what we are here for."

While Weizman declined to go into details, he indicated that peace between Egypt and Israel involves much more than just a prompt and unilateral Israeli withdrawal from the Sinai peninsula and the Gaza Strip. Gur's presentation, he said, ranged over the vulnerability of Israel's vital shipping lane in the Strait of Tiran, the isolation of its port of Eilat on the Gulf of Abaqa, and the need for "some sort of Israeli presence" at the entrance to the gulf "especially if the presence in Sharm EI Sheikh will be be changed from what we have today."

Weizman said the Israelis were asking for "butter zones, security areas and the possibilty of various types of military areas," as well as the right to keep some airfields in the Sinai, and for some assurances about what Egypt would do in the eventanother Arab country started a war with Isreal.

Weizman also said that Israel had decided not a install any new sttlements in the Sinai now, but to "strengthen" those already there, which Egypt wants dismantled.

The Israel defense minister also said that "all borders can be argued about and discussed," a reference to suggestions that Israeli might offer to trade Egypt some of its territory in the Negev Desert for the land it has settled in the Sinai.

To that Gamassi responded that "the Egyptian borders with Palestine are not open to any bargaining," reflecting the public position taken by Sadat. In fact, throughout their hour-long exchange with the press, Gamassi was more restrained than Weizman who, while admitting the diffuculties, stressed the determination of both sides to overcome them.

"I hope you are not hurrying us in asking about the results of our deliberations," Gamassi said. "The tropics we are dealing with are quite complicated. You may think everything will be settled in a couple of days but there are many problems which have accumulated over thirty years." He said the negotiations would be long, but corrected his translator when he rendered this as "very long."

But he did say that any of the Isreali ideas, except for the border trade, were rejected out of hand.

On the settlement, he said that "I cannot say that there is too much distance between our two positions. We are not so far apart. On the contrary, we are more determined to bridge the gap between our two position."

He also indicated that Egypt was prepared to accept the [WORD ILLEGIBLE] of some of the Sinai and perhaps limitations on the deployment of its troops in other parts of the peninsula - a break from Egypt's opening position that no sovereign country can accept limitations on the the stationary of its troops inside its own territory.

Fifteen monthsago, Sadat told a visiting American congressional delegation that "when Israel was created by [former Premier David] Ben Gurion, he created the theory of security. This includes that they must have borders, they have these secure borders, they have put their demand for expansion, in taking others lands by force."

Reflecting that view,Egyptian officials have refused to take seriously the idea that Israel has genuine concerns about its future security. In their view, the entire notion of secure borders for Israel was shown to be invalid by the crossing of the Suez Canal in the 1973 war. They argued that the real road to national security for Israel lay in abandoning the continued Arab hostility, and in any case Israel was a military power fully able to defend itself inside its pre-1967 borders.

But Sadat, who lies spent a great deal of time analyzing the collective national psychology of the Israelis, observed in a recent interview with a Cairo magazine that to understand that they see themselves as "surrounded by millions of hostile Arabs."

Bar Lev Line showed "the age of using high walls, sand, waterways and deserts as barriers" to insure national security "is gone forgood. Missiles and planes can reach any position deep in enemy territory."

But he added, "the Jewish people have a special problem, which we must know so as to understand their stands and learn how to adopt their decisions. The Jews have been living in fear for thousands of years."

That does not mean that Sadat is prepared to make any permanent concessions on territory or sovereighty over any part of the Sinai. On the contrary, he has stressed that he wants it all back and the Israelis must go. But it appears that he is willing to be flexible on timing on the details of the handover, allowing the Israelis to withdraw according to a timetable that will assuage their anxiety over Egyptian sincerity and the respone of their neighbors.

The military committee is scheduled to meet again on Friday, but then is apparently going to recess until after the first meetings of the joint political committee, which begin Monday in Jerusalem. No definitive decisions on the military aspects of an agreement are expected to be announced in this phase of the talks.

The negotiations here are strictly bilateral and have not dealt with the even more difficult questions of the West Bank of the Jordon ot the future status of the Palestinians, though Israel's concerns about its security on that front are for deeper than they are over the Sinai. Gamassi indicated that if the political committee can reach agreement on the future of the West Bank - still highly doubtful - then the military implications of that could be taken up in the talks here.