There are solid indications that the government of Menachem Begin, less than a week before the prime minister's crucial trip to Washington, is facing its most serious internal crisis since its formation nine months ago.

Widespread reports here yesterday said that three members of Begin's Cabinet, among them Defense Minister Ezer Weizman, had threatened to resign if the government allowed work to resume on the expansion of Jewish settlements in occupied Arab territories.

Weizman, who is now in Washington, denied last night that he had threatened to resign but he acknowledge that he and Begin had an angry transatlantic telephone conversation on the matter and "I put my foot down hard.

Weizman said in Washington that he had been assured that work on the settlements would remain suspended until after Begin ans President Carter meet for talks next week. The settlements problem would be a subject of those talks, he said, according to Reuter news service.

In his telephone conversation with Begin, Weizman said, "We did have a talk about how I look at things and how he looks at things. We both look at things in the same way now."

The issue of Iraeli settlements in occupied territories has become one of the most sensitive in the peace talks between Israel and Egypt. U.S. officials have called it a major obstacle in the talks and the United States has said repeatedly that it considers the settlements illegal.

Before Weizman left for Washington, he ordered that ground clearing and expansion of settlements be halted to improve the atmosphere for Begin's talk with Carter. When Weizman left for Washington, supporters of an expanded settlements policy began pressuring Begin for a resumption of the work.

Agriculture Minister Ariel Sharon, who opposed Weizman's directive, reportedly threatened to resign, as did Finance Minister Simcha Ehrlich, who supports Weizman's position. Both later denied the reports.

It was learned here from authoritative sources that, following his telephone conversation with Weizman Monday night, Begin consulted with several Cabinet ministers and it was decided to uphold Weizman's orders to suspend work on the settlements.

Deputy Prime Minister Yigael Yadin told reporters yesterday that "as of this morning, no work is being carried out," adding that "Weizman's orders are being inplemented fully."

In reply to another question, Yadin acknowledge that the rift between Cabinet ministers who openly question decisions made by their colleagues and contradict them in public is distrupting the work of the government.

"This cannot go on," Yadin said emphatically. He expressed the hope that a full discussion of all the subjects that cause friction will be held as soon as Begin returns from his trip tp Washington next week.

While it is too early to assess the outcome of the present clash within the Begin government, some observers here believe that while a falling out between Weizman and Begin is inevitable, the defense minister may have precipiated the confrontation prematurely and therefore both sides are attempting to minimize the seriousness of the rift.

Although the settlement issue is prominent in the clash between the two Likud party leaders, is believed also to be displeased over several other positions adopted by Israel in negotiations with Egypt. Weizman reportedly has said on several occasions that reached if the Israeli government were to play its cards properly.

The settlements issue splits not only Israel's ruling Likud Party but also the coalition Cabinet. A full-scale shodwdown is not expected until after the return of Begin. Weizman and Foreign Minister Moshe Dayan from their missions to Washington.

Begin, who had earlier refused an invitation to brief the Likud parliamentary faction, Claiming pressure of work before his departure, and the danger of leaks concerning proposals to be made to Carter, changed his mind last night, He is now expected to explain to the group in closed session the background of the present crisis.

Meanwhile, Gush Emunim, the extremist group that insists on unhindered right of settlement of the entire occupied West Bank, held a press conference yesterday and protested vehemently against the "obstacles" that the government has allegedly created to Israeli settlement in the occupied territories. Today Gush Emunim settlers and supporters are to demonstate in front of the prime minister's office in Jerusalem.

Two spokesmen of Gush Emunim, Rabbi Moshe Levinger and Dr. Ezra Zohar, claimed that even a temporary halt in settlement may be detrimental to the movement, which they term the "essence" of Zionism. They said the peace negotiation process will be a lengthy one, and can be used to block their efforts permanently.