Menachem Begin, the leader of the Likud Party that won an upset victory in last week's Israel election, was admitted to the intesive-care wared of Tel Aviv's Ichilov Municipal Hospital early this morning, reportedly suffering from overwork and fatigue.

Begin, 64, the most likely candidate to become Israel's next prime minister if his party can put together a working coalition, suffered a heart attack complicated by pneumonia before the election.

Although his doctor said he had recovered and would be able to carry a full workload, doubts still persist as to his abiltiy to carry the burdens of the prime minister's office. Begin is reportedly in no danger, but today's hospitalization is certain to increase these doubts.

Begin's doctor,Schlomo Laniado, said there were no signs of Begin's having suffered another heart attack.He said Begin had not been feeling well after yesterday's exhausting schedule, which included a lunch with the new U.S. ambassador, Samuel Lewis, and had been admitted to the hospital at 3 a.m. Dr. Laniado said Begin would be kept under observation for "a few days."

The most likely candidate to replace Begin, if he is unable to assume the duties of prine minister, would be the former chief of operations and chief of the air force, Ezer Weizman, who is currently the leading candidate for the post of defense minister.

One of the problems with the Likud Party is that for 29 years Begin has been so ruthless in suppressing possible successors or rivals that today there is a lack of talent and depth in the ranks of potential leadership.

Wiezman himself once left Begin'c Herut Party because of this, and Likud's No. 2 man, Simcha Erlich, belongs to the Liberal faction and is therefore not considered to be as close to power as Weizman, who returned to the Herut faction.

The Likud bloc, although now unified political party, is itself a coalition of former parties and factions, the most important being Begin's Herut faction, with about 18 of Likud's 43 parliament seats, and the old Liberal Party, with 16 seats.

The Liberals within Likud are aready sending signals that they are upset with some of Begin's recent hawkish statements, which have caused alarm in the United States as well as in Israel. This group is arguing in favor of a coalition with the left-of-center an dovish Democratic Movement for change to help balance Herut.

Movement leaders foresed a crisis within Likud between Liberals and the more conservative Herut. If Begin cannot lead Likud because of his health, this crisis might come sooner rather than later.

Begin's recent and repeated statements that he intends to keep the occupied West Bank, captured from Jordan in 1967, have caused dismay and apprenhsion both here and in the United States - not only within the Carter administration, but among American Jews as well. Rabbi Alexander Schindler, chairman of the Conference of Presidents of Major Jewish Organizations, is expected here shortlyto tell Likud of the mood of Washington, and others are expected to follow.

Begin's remarks on American television that President Carter, because he knows the Bible "by heart." should know to whom Judea and Samaria - the occupied West Bank - belong is seen by many Israelis,even Beginsupporters, as uncecessary and provocative rhetoric.

Both Weizman and Erlich said that efforts to from a coalition government would continue despite Begin's hospitalization.

The Likud negotiating team is scheduled to meet Tuesday with leaders of Yigael Yadin's Democratic Movement to discuss a coalition - the first of what will undoubtedly be many such meetings.

In another development, Prime Minister Yitzhak Rabin, who took a extended "vacation" during the campaign because of his involvement in a financial scandal, has decided to resume the reins of his lame-duck government, according to Israeli radio.

It would appear the Rabin is hoping to increase his influence in the Labor Party, soon to be in opposition for the first time, at the expense of Shimon Peres, whom the party chose as Rabin's successor.

Rabin will continue as prime minister fo caretaker government until a new government can be formed, a process expected to take several weeks.