Despite the near-pharaonic power that cloaks President Anwar Sadat these days, the smug American assumption that Egypt is inextricably locked in as America's faithful, stable ally rests on future events that even Sadat himself cannot fully control.

"Under Sadat," one Egyptian political operative told us, "We have become more pro-American than you Americans." That verdict is unarguable today. The courageous Sadat's latest agreement with President Carter to let Israeli Prime Minister Menachem Begin once again have his way on procedures to unblock West Bank autonomy talks is proof enough of that.

But while Begin continues to obstruct real autonomy for the Palestinians, Sadat faces far worse dangers at home only marginally affected by what happens on the West Bank; ravaging inflation, particularly high food prices; a disturbing trend back toward Moslem fundamentalism; and -- however much denied -- growing political hazards from Egypt's isolation in the Arab world.

The key to Sadat's skill in protecting his pharanoic dimension lies squarely on the economy. But giddy promises of the good life held out to the Egyptian people as Sadat tied Cairo ever tighter to Washington have fallen dangerously short of expectations.

"Anwar sits on an inflation powder keg," a Western authority on internal Egyptian politics told us. Explosion of the powder keg would engulf Sadat first and might even doom Carter's whole Mideast peace eneterprise that started with Sadat's 1977 visit to Jerusalem. Moreover, if the price of food continues to outpace wages and government subsidies, resentment over the economy will inflame the issues of Moslem fundamentalism on the right and anti-American pan-Arabism on the left, possibly fusing them for the first time.

Warning signals have been emanating from the government of highly esteemed Prime Minister Mustafa Kahlil. Last week a long and remarkable tract signed by Sadat himself was published in major newspapers. It defended Egypt's historically leading role in the Arab world, particularly since the 1952 Nasser revolution of independence.

Justifying the Camp David accords, Sadat said that "no Arab country save Egypt had either the determination or the ability to take that initiative." Furthermore, he insisted, differences over Camp David with "the arab 'rejectionist' rulers are only tactical, not strategic; temporary, not permanent." Egypt remains "the heart and the vanguard of the Arab nation."

The voluminous Sadat treatise follows nearly two years of Egypt's estrangement from the Arab world. It is an appeal to pan-Arab Egyptian nationalists for patience. It is also a declaration of concern over Egypt's continuing exile.

Another signal of problems ahead was the government's last-minute decision early this year not to reduce costly food subsidies. With prices moving up at least 30 percent a year and wages in effect frozen, a subsidy cut would set off immediate riots in large cities.

Still another portent of home-front danger is the veiled press attack -- clearly government stimulated -- against leaders of the Coptic (Christian) religion, a sizable, potent minority. Moslem resentment of the Copts was a factor in the recent student riots in upper Egypt, as was Sadat's brave and uplifting decision to take in the shah of Iran, regarded by some Moslems as an enemy of Islam.

In dealing with the drama of peace with Israel, Sadat displays stunning versatility. He absorbs one Begin shock after another without undue complaint. Begin's West Bank invasion-by-settlements and his foot-dragging against Palestinian autonomy are viewed here as temporary: their solution will come when Israeli voters turn out Begin and elect a new government.

Thus, even though Begin has soured feelings here on the normalizing of relations with Israel, Sadat has overruled advisers and moved ahead of Camp David timetables. The direct Cairo-Tel Aviv air link is now operating, far ahead of the July 26 deadline set in the Camp David accords.

But that fast track on Egyptian-Israeli peace is easy going compared with rising tempers over runaway food prices, which in turn will directly infect the disturbing phenomenon of Moslem fundamentalism and Cairo's exclusion from the Arab world it used to lead. That explains why the prayer rugs are getting a heavier workout for price stability by far than for West Bank autonomy -- for most Egyptians, a faraway problem with little bearing on the hard business of living.