"There is no god but Allah, and Mohammed is his prophet."

In recent months, the medium for this basic Islamic message had been battered bumpers and dusty windshields all over Cairo. Everywhere, it seemed, decals of elegant Arabic calligraphy made this fundamental proclamation of Moslem faith.

But no more. Last week all windshield and bumper stickers were banned. Today, enforcement of the law began. By late afternoon religious stickers were scarce.

In other circumstances, the ordinance might have seemed trivial. But in a nation where the public mood is more often read by symbols than by polls, the stickers had come to be viewed by some analysts as a kind of rolling plebiscite on the role of religion in this society.

So as the secular government of President Hosni Mubarak began a political counteroffensive against the growing demands of Islamic fundamentalists, the stickers became another skirmish line.

The stickers first showed up about a year ago in apparent response to Coptic Christian decals. The Copts, an influential minority, had displayed pictures of their pope, Shenouda III, when he was exiled in a desert monastery. They pasted crucifixes to their vent windows. One iridescent decal read, in English, "In God We Trust."

The Islamic "no god but Allah" decals soon overwhelmed the Christian symbols. Every taxi seemed to have one. Mercedes, Peugeots, beat-up old Buicks, all bore the creed of Islam.

Editorialists in the semiofficial press began to worry about potential disaster if a Shenouda-stickered Fiat should crash into a "no god but Allah" Datsun.

During the spring, as the bumper-sticker war was building, on more obvious fronts Mubarak had seemed reluctant to clash with the many groups demanding immediate implementation of sharia, or strict Islamic law, throughout Egypt.

Mubarak's predecessor, Anwar Sadat, tried alternately to co-opt and then to repress religious dissidence. Sadat was killed by Islamic extremists in 1981.

Mubarak has tried to create at least the semblance of a democratic opening here, including free speech. Within the space he allowed, the fundamentalists appeared steadily to be gaining political momentum.

Although many moderate Moslems displayed the stickers, their pervasiveness often was cited as evidence of fundamentalist strength.

But in early June, faced with the challenge of a mass protest march called by fundamentalist Sheik Hafez Salama, Mubarak banned the demonstration and put thousands of riot police in the streets around Salama's mosque to prevent any attempt at an unauthorized march. Last week, Mubarak put Salama's Al Nur Mosque directly under state control.

Meanwhile, despite the desires of some fundamentalists to see laws governing marriage revert to the patterns of 50 years ago, Mubarak's parliament passed new legislation guaranteeing basic marriage and divorce rights to women.

During the Beirut hijacking crisis Mubarak sharply denounced extremists in contexts that clearly aimed his remarks at the fundamentalists. This was echoed relentlessly in the semiofficial press.

Having asserted himself on those more crucial fronts, Mubarak then moved to the matter of the stickers.

Keeping with his pattern of strong statements and shows of force but moderate action, his government promised to suspend for a year the license of any driver caught today with any sticker.

Pope Shenouda himself called on Christians to strip off their decals. Some Moslem scholars also called for an end to the sticker displays.

Many Moslem drivers appeared to be resentful, some complaining that it seemed a sacrilege to scratch out "No god but Allah."

"Christians and Moslems are the same," said Helmi, a suburban cab driver with a decal. "It's just the government causing problems."