Most of the free-spending Persian Gulf Arabs who boycotted Egypt after last year's Egyptian-Israeli peace treaty are back on vacation in Cairo again, enjoying the city's tolerant night life far from the austerity of their own conservative countries.

Their white robes and headdresses can be seen in growing numbers at Nileside cafe tables around roulette wheels in the city's two authorized gambling casinos and at festive iftar meals organized by Cairo restaurants to break the daylong fast prescribed by Islam for the current month of Ramadan.

The official Arab boycott is still in place, however, and the governments of the Persian Gulf show no sign they are ready to resume contacts with Egypt until the disagreement created by Camp David is resolved. At the same time, Egyptians point out, travel restrictions were never imposed officially. Among the vacationing public in Saudi Arabia, Kuwait and the United Arab Emirates, last year's reluctance to be seen in Egypt apparently has dissipated.

THE INCREASING return of Arab tourists, aside from its financial blessings on Egypt's street people, is a welcome sign for Egyptian President Anwar Sadat's contention that the boycott is only temporary. It also is another sign -- along with continued private business transactions, airline connections and $2 billion a year in remittances home by Egyptian workers employed mostly in the gulf -- of the effectiveness of the boycott.

The Egyptian Ministry of Tourism reports that the number of Arabs entering Egypt in June was nearly double that of a year ago, up to nearly 70,000. Statistics are not yet in for July and August, but ministry officials and other observers noted a sharp increase during Ramadan, which began in July and recently ended.

The number of Arab tourists falls far below that of European and American visitors. But the Arabs are particularly welcome because of their political significance and the amount of money they spend. Ministry officials say Europeans stay seven days on the average, at about $70 a day, while Arabs stay several weeks and spend hundreds of dollars each day.

Ramadan is the favorite month for Arab tourists to visit here. Particularly in years such as this when it falls during summer, by traveling to Cairo they escape the stifling heat and humidity of their own countries on the Persian Gulf. They also avoid the Islamic strictures that prevent them from drinking, gambling and enjoying other nocturnal pleasures readily available in this city of 10 million.

DESPITE EGYPT'S strong Islamic tradition, Egyptians turned the fasting of Ramadan into a prelude for nightlong feasting. Crowds celebrate into the night at restaurants and cafes and in the garish nightclubs that line the four-lane avenue to the Pyvamids. Wealthy Arabs pay up to $40 for a bottle of whiskey and a motley floor show of belly dancers and "European specialties."

This has been a tradition here since the rush of oil money created millionaires along the Persian Gulf. Because of last year's political boycott, however, the number of Arabs vacationing here dropped sharply.

At the Sheraton Hotel beside the Nile, for example, the Arab clientele that usually amounted to half the guests had shrunk to less than one-third. This year, reports public relations director Rashah Murad, the proportion is back up to half again.

"The Saudis apparently are no longer telling their nationals not to come," he said. "The boycott lasted one year."

Saudis in their distinctive white robes or, for younger men, western blue jeans and open-necked shirts, were nearly half the audience one night during Ramadan as traditional singer Mohammed Taha bobbed and weaved under his fez through a repertoire of Egyptian songs in the Sheraton's incense-filled coffee shop. Upstairs at the casino, Saudis, Kuwaitis and other Gulf Arabs took their places at the gaming tables along with Europeans and Japanese.

DESPITE THE SPECTACLE of a gray-haired Kuwaiti in a white robe with matching shoes shoving two-inch-high stacks of chips around the roulette table the other night, Murad said the number of Arab high rollers remains small. This apparently reflects a continued snub by prominent or politically important Arabs whose reputation would be endangered by an appearance at a Cairo night spot.

Even the less prominent and less wealthy Arabs, however, are favorites with the Cairo taxi drivers and fixers who make their living from tips, or baksheesh. Gulf Arabs traditionally are charged significantly higher prices than Egyptians or even other tourists, and they have a grand reputation here as high tippers.

But Mohammed Abdullah, a taxi driver stationed outside the Sheraton, said the reputation often is unjustified, and he and his colleagues frequently quarrel with Saudi clients who complain of being overcharged. Even though the tips are smaller, Abdullah said, he prefers European tourists with traditional itineraries such as the Sphinx, the Pyramids and the Cairo Museum.

"The Arabs are all crazy no-accounts," he said. "Too much petroleum. Too much money. All they want is hashish and girls."