Israeli Prime Minister Menahem Begin's minority Likud Party is riding a wave of post-election popularity despite three run-ins with Washington over the occupied West Bank.

The opposition Labor Party's warnings of impending diplomatic isolation go unheeded following Secretary of State Cyrus Vance's recent unfruitful discussions here.

A high point to the nine-week-old Begin administration's honeymoon with the Israeli voter came during the prime minister's trip to Washington. In Israeli eyes, the right-wing politician managed to steer a course independent of theAmericans without causing a confrontation with Tel Aviv's one indispensable ally.

Since Vance's visit, doubters, especially in Labor Party ranks are beginning to question whether Begin really got away with it.

These doubts were recently expressed in a Jerusalem Post editorial that said Begin "is dissembling when he seeks to make it appear that the present situation is no more, indeed far less, a cause for concern than was Mr. Ford's reassessment in 1975 and Mr. Carter's savage lecture to Mr. Rabin earlier this year. While disharmony is virtually at a peak of harshness Mr. Begin pretends to hear little except the sounds of sweet concord." That alone, the paper said, "is reason for anxiety."

The doubts among some opinion-makers, however, have not sifted down to the population at large, and the honeymoon between Begin and the Israeli public continues.

Begin's position of refusing to return to Israel's pre-1967 borders or to deal with the Palestine Liberation Organization is unquestionably shared all the major political parties except the Communists.

As for his position that Israel should not surrender territory on the West Bank and Gaza Strip even for peace, the opposition Labor Party's restrictions on what could be given back were so narrow and circumscribed that they too were unacceptable to the Arabs.

Begin's three moves to consolidate Israels position on the West Bank following his visit to Washington appear to some Israelis as a poke in President Carter's eye. In succession, Begin legalized three Jewish settlements on the West bank, promised to equalize services between West Bank Arabs and Israeli citizens and then announced that three more Jewish settlements were to be established on the West Bank.

A high government official hinted that the three new settlements may be only the beginning and that more may follow shortly.

Begins explanations that he was only following up decisions made by the previous government or that his moves were made solely on humanitarian grounds appear to some Israelis as disingenuous. "It seems as if he is trying to trick President Carter," one Israeli said recently.

But the majority of the Israelis appear to feel that Begin is doing a better job than his predecessor, Yitzhak Rabin, in maintaining good relations with the Americans while at the same time standing up for Israel's interests.

"I am absolutely crazy about him," a refreshment stand owner said. "In my eyes Begin is the equal to Ben Gurion. The only problem is his ministers. If only they were all like Begin."

Begin's team of ministers is still feeling its way and it is much to early to judge its performance. But it is already very clear that Begin ad Begin alone is the government.

"This is the closest thing that we have ever seen to a presidentil system of government," an official said recently.

One no longer hears complaints about of lack of leadership, which were often heard when Rabin was prime minister.

Although Begin seems to thrive on hard work and long hours, he did have a serious heart attack shortly before the election and there is private worry among his supporters that he may overtax himself too hard. "It is inconceivable to imagine a Likud government without Begin," a member of Parliament said recently.

Although Begin enjoys only a slim majority in Parliament, his position is firmer than it seems because the opposition is in such disarray.

It is often said that Begin's government has no experience with running the country because it was in opposition for 30 years. The reverse, however is also true: The Labor Party, which had ruled Israel since independence, has had no experience in opposition. Opposition members are quarrelling among themselves, and the opposition case is not being presented in a persuasive or coherent manner.

Yigael Yadin's new party, the Democratic Movement for Change, is in even worse disarray, having entered into coalition negotiations with Begin twice only to break off the talks each time.

"There are splits in decisions all over the party," one member said.

One cannot accurately predict whether Yadin's party will eventually join the coalition, but eyes if it does not, no one seems likely to unseat Begin in the near future.

The darkest clouds on the government's horizon have to do with domestic legislation rather than foreign affairs. Begin needs the ultra-Orthodox religious parties to keep his parliamentary majority, and sooner or later they are going to ask for strict legislation on religious matters that many secular Jews will find offensive.

Another cloud is the economic situation, on which the new Likud government has not yet had time to prove's itself. Yet a recent poll showed that 65 per cent of the people queried thought that the government is doing a good job on economic matters. Only 15 to 20 per cent thought the old government had done a good job on economic matters.

Begin's real interests lie with matters of peace rather than domestic problems, and if trouble comes it is likely to come from the United States to allow him to go promptly to Geneva to negotiate with the Arabs. If the talks should end in deadlock he will have demonstrated willingness to negotiate.

The Americans, on the other hand, see a last chance to nudge the parties toward an agreement while American influence in the Middle East is at its peak. In short, the Americans feel that the issue is much too serious to be left to the Arabs and Israelis.

But the change of government that Begin's election brought has probably broken forever the undisputed power of the old labor establishment. The Labor Party may be back again one day, but probably never again on the same terms.

News agencies reported the following:

Israeli Foreign Minister Moshe Dayan took off from Tel Aviv Monday for what Prime Minister Begin suddenly announced would be a 24-hour visit to London. Dayan denied rumors of a secret meeting with king Hussein, who is vacationing in England. Dayan failed to show up in London, and French radio reported that he had spent five hours in Paris.

Palestinian sources in Beirut say Britain broke with past practive Monday when James Craig, London's ambassador to Syria, say down for a talk with Khaled Fahoum, an official of the Palestine Liberation Organization. Craig said the meeting had not been a formal call. Britain previously followed strictly the U.S. policy not talking to Plo officials.