When the Egyptian flag went up over the Sinai town of El Arish this morning, in a ceremony televised live across the country, it marked a proud and important moment of vindication for President Anwar Sadat.

Spurned and scorned by his fellow Arabs who accuse him of making a separate peace with Israel, Sadat argues that his approach is the only one that produces any results. The Israeli evacuation of a big chunk of Arab and that they held for almost 12 years reinforces his position and gives the Egyptian people, anxious and restive about their isolation from the Arab world, cause for celebration.

El Arish, an obscure, dusty town of 80,000 residents, is of little intrinsic importance and its reacquistion will be an economic burden on the Egyptian treasury. But the government has made prodigious efforts to ensure that this weekend's events receive maximum publicity, not only in Egypt but throughout the Middle East, because of the symbolic importance of the Israeli withdrawal.

Sadat wants the hundreds of correspondents and cameramen - including one from the Saudi press agency - to deliver once again his solitary but determined message to the other Arabs: Slogans do not liberate Arab land, rhetoric does not oblige the Israelis to negotiate over autonomy for the Palestinian people whose existence they once denied; only my way, the way of direct negotiations, brings any results.

"The stance of our Arab brothers is known to us all," Sadat told French journalists this week "They have endorsed a peaceful solution to the Middle East conflict at the Baghdad conference [last November]. We differ with them because they depend only on radio speeches to reach this goal."

Sadat used the same argument after he signed disengagement agreements with Israel after the 1973 war, saying that he was liberating Arab land from Israeli occupation without further bloodshed and without giving up long-range claims on the West Bank. That argument was unavailing then and the agreements brought him furious criticism from the other Arabs, but that did not deter him from going ahead with his peace initiative. Nor is it likely to do so this time.

The other Arabs-especially Syria, Jordan and the Palestine Liberation Organization-say Sadat played into Israel's hands by dropping out of the struggle against the Jewish state and getting in return only what Israel was always willing to give, namely the Sinai.

Sadat believes that the other e, namely the Sinai.

Sadat believes that the other Arabs basically share his desire to end the fruitless confrontation with Israel and make peace on honorable terms. Many of them have said so. Sadat, however, also believes that they are political cowards or so constrained by domestic pressures in their own countries that they are paralyzed when it comes to real negotiations.

"If they really want a peaceful solution, they have to sit with the Israelis as I did," Sadat told the French reporters the other day. "If they prefer Geneva, then I am ready to go to Geneva tomorrow morning, but they will reject this because they have no alternative to the negative policy of the past 31 years. This seems to be the easiest thing to do, . . . to remain in their seats and exploit the situation."

Sadat and his advisers argue that their approach not only has regained Arab land but also has made the objective of Palestinian independence and Israeli withdrawal from the West Bank "at least more possible than they were before," as one of Sadat's top negotiators put it this week.

So Sadat will press ahead, first in the negotiations over Palestinian autonomy that begin this weekend, then in an Islamic conference he is planning in December to discuss the future of Jerusalem. If nobody comes, he will probably unveil his proposals on the Jerusalem question anyway, and negotiate over them by himself.

Sadat knows this is a hazardous course, especially as the Israelis embarrass him by bombing in Lebanon and establishing new settlements in the West Bank. That is why, in the Egyptian view, ceremonies like the handover of El Arish and the next one of the Sinai oil fields, and the promised deliveries of American weapons, are important. Sadat needs periodic moments of tangible, in-hand success for his policy in order to keep it going. CAPTION: Picture 1, ANWAR SADAT . . . cites results; Picture 2, Soldiers lower the Israeli flag in a ceremony marking the transfer of the Sinai town of El Arish to Egypt. AP