Prime Minister Menachem Begin postponed his departure for the United States last night following a Palestinian terrorist attack inside Israel that injected a new element into the Middle East equation.

Israel's Defense Minister Ezer Weizman, who was in the United States waiting to join Begin for talks with President Carter, cut short his visit and flew home.

American officials said last night they expected Begin would arrive here for talks Tuesday.

Before leaving New York, Weizman seized on the grim tragedy to remind Americans of "the security problem Israel has [in] having unfriendly territories near us."

"How many times does it take to prove that we have problems living in a secure land. This is what can happen when certain close areas will be, or can be, controlled by the Palestine Liberation Organization," Weizman said.

"It's the most savage, worst attack in the last 30 years within our borders," he said. "Israel will take such action that things like this will not happen again."

There were no indications last night whether Israel would mount retaliatory strikes against Palestinian strongholds in Lebanon as it had done following previous terrorist attacks.

A new outburst of fighting in the area would further complicate U.S.-Israeli relations.

Weizman said, however, that he did not expect that the incident would affect the current negotiations between Israel and Egypt.

In Cairo, the Egyptian Minister of State for Foreign Affairs, Boutros Ghali, also expressed hope that the incident would "not stop the process of peace" in the Middle East.

But the terrorist attack, for which the largest Palestinian guerilla group, Al Fatah, claimed credit - clearly seemed designed to scuttle negotiations towards a Middle East settlement.

Coming on the eve of what were shaping up as showdown talks between Carter and Begin, the attack could conceivable stiffen the Israeli leader's resistance to making territorial concessions.

The Carter administration was preparing to take a tough stand in this week's talks on the need for Israeli withdrawal from the occupied West Bank of the Jordan River and from the Gaza Strip. The Begin government has vigorously opposed withdrawing from the West Bank on security grounds.

The magnitude of yesterday's tragedy, however, provides the Begin government with a vivid argument to buttress its insistence on adequate security arrangements.

President Carter, in a statement, condemned the terrorist attack as "cowardly and senseless."

"This brutal act of terrorism will surely be met with universal revulsion by all men of conscience," Carter said.

In a personal message to Begin, which was delivered by U.S. Ambassador Samuel Lewis, Carter asked the Israeli leader to give his personal condolences to the families of the victims.

"I am particularly distressed that an event such as this should occur just as you were preparing to depart on your mission of peace," Carter said. "I continue to look forward to talking to you soon and relaying to you in person the deep emotions which this event has aroused in this country."

A similar statement was issued by Secretary of State Cyrus Vance who said the perpetrators of the attack "should receive the punishment they deserve."

State Department officials said last night they had not been officially notified of the delay in Begin's travel plans. He was scheduled to arrive in New York today and come to Washington Monday afternoon.

As of last night, Begin's departure had been delayed by at least 24 hours.

Begin had been embarrassed in recent days by well publicized internal arguments over his policy toward Israeli settlements on the occupied territories.

The terrorist attack yesterday, thus gave a fresh jolt to the Begin government.

Some Israelis, however, felt the attack would make it easier for Begin to press the case for Israel's security needs.

"This tragedy," Weizman said, referring to Israel and the United States, "will bring us closer together."