Egyptian President Anwar Sadat is negotiating at the Camp David summit on the Middle East prepared to push for a total failure of the talks rather than accept a half-success or what he sees as a cosmetic arrangement that does not give him the minimum he needs to refurbish his credentials in the Arab world.

That at least was Sadat's plan going into the summit, and was the calculation that lay behind his description on Tuesday of the summit as "a crucial crossroad," according to Egyptian officials who are not involved in the secret meetings.

Sadat, President Carter and Israeli Prime Minister Menachem Begin have all entered the talks eager to make them succeed, and the fragmentary accounts of the atmosphere around the first three days of the summit strongly suggested that some progress already has been made, at least in lowering tensions.

But the three leaders also have come into the meeting with detailed sets of options that include the possibility of failure. One of Carter's top Middle East experts was routinely assigned the job of thinking about what lies ahead if the conference should collapse.

For Sadat, however, a summit failure is not simply a possibility that has to be prudently planned for along with the chances of success. For Sadat, failure is in one sense an acceptable tactical goal.

This view was echoed in comments made by some top Sadat aides before the summit began, and by the state-controlled Egyptian press as Sadat arrived here. It also is featured prominently in the corridor conversation of Egyptian journalists who, like their American and Israeli colleagues, are totally shut out of the summit talks.

"If there is a complete failure that is open and very clear, then at least Sadat can go back into the Arab political establishment" said one Egyptian writer who is keenly aware of official Egyptian thinking. "He just cannot continue to hang out on the limb by himself, as he has since he went to Jerusalem. He needs above all to have the result clear, and clearly understood, whether it is success or failure."

In issuing the invitations to the summit, which went into its fourth secretive day yesterday, Carter asked both leaders to come ready to be flexible and to make decisions.

Begin has repeatedly said that an agreement to continue talks at a lower level would be a successful outcome for the summit, and U.S. officials have echoed this view.

Sadat has rejected it, Amplifying on Sadat's stand, Musa Sabri, a commentator for the Cairo daily Al Akhbar who is close to Sadat's line of thought, wrote on Aug. 27 of "a reservation of which the United States and Israel are well - that Anwar Sadat will declare to the whole world and to the Arab people all the facts, whether the conference succeeds or fails. Should the conference fail, however, it would mean the beginning of a new, serious era."

The Egyptian desire for a clear-cut result of success or failure to end Sadat's increasingly dangerous isolation was also signaled in an interview given by Sadat's minister of state for foreign affairs, Butrous Ghali, last week to the French daily Le Monde.

If Sadat gets a statement of principles on the Palestinian problem and other issues that he thinks is acceptable to the rest of the Arab world, "before continuing negotiations we would submit the Camp David results to our Arab partners, so as to enlarge the circle of negotiators if possible and above all obtain an Arab consensus," Ghali said.

Arab diplomats and newspapers have reported over the past three weeks that an open failure would trigger a move by Saudi Arabia to convene an Arab summit at which Sadat would formaly end the daring initiative he launched last November by visiting Israel.

One sign of the pressure that Sadat faces came last Saturday from Jordan's King Hussein, the key figure in enlarging Arab-Israeli negotiations. Hussein said he has "made it clear" to Sadat "that we will not be led by vague statements and announcements which do not include clear proof that Israel has changed its attitude . . . I have informed my brother Arab leaders of our convinction that the future phases must witness the return of all the Arab sides to the circle of joint and coordinated Arab action."

U.S. diplomatic analysts do not expect Sadat to make any immediate radical changes even if the Camp David talks fail. They feel that Sadat will at some point return to peace negotiations in one form or another.

War is not a credible option for Sadat in the short term. Israel's military superiortiy over the Arabs at this points is overwhelming, and Sadat's embittered relations with the Soviet Union deny Egypt access to the only likely source of a major new influx of weapons.