Put off by the peace treaty with Israel, the Persian Gulf Arabs, whose free-spending summer vacations ordinarily delight Cairo's bakhsheesh brigades and enrich the nation, seem this year to be snubbing the night clubs and Nile breezes of Egypt.

Optimistic Egyptians say never mind, they are just late this year, or at worst will be back as usual next July and August when the Arab furor against President Anwar Sadat dies down. Catty Egyptians suggest they have all gone to Bangkok, and would have anyway because the women there are looser.

More sober Egyptians, however, assess the sharp drop in the number of Arab tourists here as part of the price of peace, a price paid through the Egyptian economy from apartment owners and hoteliers down the line to waiters and the swarms of Cairo street people ready to provide any service, real or imagined, for a consideration, or bakhsheesh.

In a paper prepared for the recent economic summit conference at Tokyo, the Egyptian government estimated tourism proceeds will decline by 50 percent this year from the $688 million registered in 1978, largely because of the Arab boycott.

Most observers, foreign and Egyptian, regard this estimate as an exaggeration. The overall number of tourists for the first four months of this year was slightly up, to more than 335,000, they point out, and luxury hotels still record occupancy rates of more than 95 percent.

But this is only part of the story. Egyptians know there is a big difference between the French couple spending a week with a tour group looking at the Pyramids and the Sphinx and the Saudi setting up summer headquarters in a suite of rooms with his family and retinue.

Europeans and Americans come mostly in the winter. They spend an average of seven nights, spending slightly more than 50 Egyptian pounds, or about $72 a day.

The Arabs - Saudis, Kuwaitis and wealthy residents of some emirates - traditionally come in July and August to escape the Persian Gulf's heat and humidity and taste the pleasures of Cairo's nightclubs, gambling casinos and other attractions forbidden by their Islamic governments.

The Ministry of Tourism estimates they spend two or three weeks on the average. Ministry officials claim they do no know how much the Arabs spend, but the taxi drivers waiting for work at the entrance to the Sheraton hotel have their own ideas about that.

"They are crazy.They run around in every direction. They don't have any program when they get here," one of the drivers said. "The Europeans and the Americans are better."

"You are out of your mind," shouted a colleague, Abdul Al. "Since they haven't been showing up, I'm operating at half-speed."

Running through their remarks was the kind of condescension that often springs up among those who cater to wealthy but not necessarily sophisticated tourists. Other Cairenes have expressed relief that the rich Arabs no longer seem to be driving up prices or monopolizing taxis and waiters with their generious tips.

An editorialist in the English-language Egyptian Gazette wrote recently that it was nice this summer to be able to get served within a reasonable interval in the city's restaurants. He added that "you no longer have to put a hanky on your head and pretend you are an Arab to get a taxi to stop for you."

The Sheraton, which lies beside the Nile near Sadat's Giza residence, has been the Arab's favorite Cairo hotel. Rashad Murad, the Sheraton public relations director, said Arabs accounted for more than half the hotel's clients at this time last year, but are down to less than 30 percent this year.

Partly as a result, the Sheraton casino is less crowded than it was been in a long time, those with Cairo experience say, and the high-stakes roulette players with wafer-thin Piaget watches and Kuffiyeh headdresses seem rare.

Ahmed, kitchen boy at the Ali Baba Night Restaurant on night club row near the Pyramids, said the Saudis do not seem so plentiful this year for the club's attractions, advertised at the entrance as: "Eastern and Western programme, with extra lunch."

The reason it makes a difference was demonstrated when a Saudi pulled up in a black Mercedes with his wife and daughter and began unloading suitcases into a furnished apartment next to the Ali Baba.

Ahmed streaked to help carry the bags. He returned five minutes later, a smile on his face and a tip in his pocket. At the same time, the Mercedes driver pulled away smiling at the wad of banknotes in his hand.

Europeans and Americans, most of whom travel in organized tour groups, cannot match the legends created by such Arab tippers.

"They mostly want to see the Pyramids, the Sphinx and go to the museums," Murad said. Generally, they do so in prepaid buses in the company of a prepaid guide.

Their numbers are growing, however, and the Egyptian government forecasts that tourists of all kinds could bring in more than $1.7 billion dollars by the early 1980. Before the Arab boycott, tourism was Egypt's fourth source of foreign exchange, bringing in 10 percent or total foreign receipts after oil, cotton and remittances from Egyptain workers overseas.

Adel Tahir, undersecretary for promotion at the Tourism Ministry, said it is too early to tell how these figures will be affected by the new Arab reluctance to summer in Cairo. Arab governments have imposed no official restrictions, he noted, and the atmosphere could clear it negotiations with Israel on Palestinian autonomy produce encouraging results.

In the meantime, Egypt has discovered a new modest source of tourist income in Israel. An Israeli travel agency working in tandem with an Egyptian agency is bringing weekly tours to Cairo, advertised as the first such regularly scheduled tours to take travelers directly from Israel to Egypt.