The assassination of Egyptian President Anwar Sadat plunged Israel into doubt and foreboding tonight about the future of Middle East peace, as Israeli leaders anxiously sought signals of continuity of the historic peace process that in 1977 ended three decades of warfare between the two nations.

Israeli Prime Minister Menachem Begin, ashen-faced and his voice quavering with emotion, emerged tonight from an emergency meeting with his senior Cabinet officials and said that he prayed that the first rapprochement with an Arab power would not also die at the hands of "the enemies of peace."

Across a broad political spectrum, Israeli leaders expressed shock and outrage over Sadat's assassination, calling it an affront to the spirit of peace that marked the Egyptian leader's visit to Jerusalem in November 1977.

Despite the pledge by Vice President Hosni Mubarak on Egyptian television that "we will continue in the name of the spirit and soul of our leader and our constitution that we will abide by all treaties and commitments made," Israeli politicians warned gravely that the assassination may have placed in doubt the final stage of the withdrawal of Israeli forces from the Sinai Peninsula, which Israel captured in the 1967 six-day war.

Extreme nationalists in Israel's Parliament immediately seized upon the assassination as a reason for abrogating the 1979 Israeli-Egyptian Camp David peace accords and cancelling the withdrawal from the last third of the Sinai, which is scheduled to take place April 28.

Officially, the government responded in a moderate way to the announcement in Cairo that Sadat had died in the attack during ceremonies marking the anniversary of the October war.

Begin sequestered himself and his closest advisers for more than four hours in his private residence, refusing to comment on the implications of the slaying until well after the official announcement was issued.

Even then, his comments were more of a tribute to Sadat as a peace-maker and friend than an indictment of Israel's enemies or a dark assessment of the future of peace in the region.

"The criminals assassinated one of the great fighters for peace in our generation," Begin announced in an occassionally breaking voice. "The people of Israel share in the mourning of the Egyptian people for those who fell victim to the enemies of peace."

Begin recalled that the entire free world rejoiced over Sadat's 1977 visit, and that the world, similarly, would grieve over his death. But, Begin said, the peace process will continue "as President Sadat would have wished it would continue, despite the efforts of the enemies of peace."

There were similar expressions of cautious optimism from other Israeli leaders, but also indications of doubt over whether Israel can maintain a semblance of momentum for peace without the chief architect of the Camp David process.

Former foreign minister Moshe Dayan said the assassination "puts a very big question mark about the continuation of the peace treaty because of [Sadat's] personal rule. You cannot ignore the personal rule of Sadat. If Hosni Mubarak or the others will be as strong as Sadat was and will honor the peace treaty and all the commitments, then I think things will go according to the peace agreement," Dayan added.

Former prime minister Yitzhak Rabin, now in the Labor Party opposition of the Knesset (parliament), also said the assassination "will have a lot of influence on the peace process."

"When you make peace with an Arab nation, it is very important with which leader you make the peace, and how long the leader remains in office. It will take some time until we find out what are the tendencies of his heir," Rabin said.

As strongly as supporters of the peace process lamented the effects of Sadat's death on future negotiations, opponents seized on the assassination as an opening for cancelling the Sinai withdrawal and the planned dismantlement of Jewish civilian settlements there.

Barely two hours after the first reports of the Cairo shooting, supporters of the ultranationalist Tehiya Party appeared in front of Begin's house with placards and petitions demanding that the Camp David accords be abrogated.

One of Begin's closest advisers, Yeheil Kadishai, director-general of the prime minister's office, said that while many Israelis were naturally concerned about the peace process, it was the wrong time to question the validity of Israeli plans to withdraw from the Sinai.

Burg said that Sadat was so essential to the peace process because he knew the complexity of the problem, and at the same time understood Israel's deeply engrained need for security.

Sadat, Burg said, had three basic inclinations: to remain firmly within the sphere of Western democracies, to work for peace and to alleviate poverty in his own country.

"These are the three big visions he maintained with all his heart. I can only hope his successors will go in the same direction," Burg said.

As Israeli leaders sought to come to grips with the enormous implications of Sadat's death, there were recurring questions of whether Mubarak could demonstrate the same degree of personal authority, or whether he would be intimidated by the assassination and backpedal from the Camp David commitments.

Sadat has always been perceived here as running a one-man government, dismissing political opponents from his inner circle with ease but at the same time leaving himself and Egypt without a natural successor.

Mubarak is widely considered a pliant follower with few strong convictions of his own. Although Israelis are keenly mindful that Sadat, as vice president to Gamal Abdel Nasser, was once viewed in the same light, there still are strong reservations that Mubarak has the same leadership potential.

In an interview in July with The Wall Street Journal, Begin hinted at the effects of succession on the peace process, saying, "President Sadat is as mortal as I am. We both of us one day will disappear from the scene. And then maybe the other ruler will change his mind. That may happen."

But, Begin went on to say, "that may happen everywhere. Everywhere. So I consider the peace treaty to be a very serious and a very great achievement. Good for Israel, and for Egypt and for the Middle East and for the world at large. After 32 years of a state of war, activated in five wars, in which thousands of people died, for the first time in that generation we signed a peace treaty."

Saying he expected the terms of the accords to be fulfilled in April, the prime minister added, "So why should I make prophesies? We shall see. Maybe still I will be prime minister until then, and you will come again to me and ask the question."