A spate of local disasters this month has brought home to Egyptian authorities and 12 million Cairenes alike just how fine a line this ancient Nile Valley city, engulfed today in humanity, is walking on the precipice of environmental catastrophe.

In early December, a major sewer main, rusted with age, overworked and unattended, finally burst on the west side of the river dividing the capital in the middle-class district known as Giza. This is where the famous pyramids and a good number of fancy nightclubs and tourist hotels are located, together with about 3 million Egyptians.

The result was a flooding of streets, byways and homes the likes of which Cairo, which has been through a lot in its 1,000-odd years of glories and defeats, has not seen for decades.

Lakes of sewer water sprang up overnight in some low-lying sections of Giza and the neighboring Dokki and Mohandessin districts. In others, residential areas have been turned into a scene reminiscent of Venice with its crisscrossing canals running between rows of buildings.

With no place to go in an already vastly overcrowded city, few Cairenes have abandoned their homes, leaving owners or occupants to cope as best they can with the filthy water and stench.

For unknown reasons, sewer water also began bubbling up here and there in the downtown area of the city on the east bank of the Nile, apparently resulting from a backup in the whole system.

BUT THE TROUBLES did not stop there. City authorities, to stem the runaway sea of sewer water, cut way back on the water supply to reduce the pressure. As a result, hundreds of thousands of denizens of these neighborhoods also found themselves with little or no drinking water.

The water shortage, in turn, provoked a crisis for bakeries, which could not turn out their usual mountains of flat disks of bread, known as aiish baladi, which, together with fava beans, is the mainstay of the poorer classes. It is also a key to the political stability of any regime in Cairo.

The government, fully aware that bread is far more important to its survival than the outcome of Middle East peace talks, went on full alert. President Hosni Mubarak made it known that a hasty repair of the sewer main was a top priority and ordered progress reports every four hours.

The first reports said repairs would be finished in a few days. But since then each day has brought a new readjustment in estimates of when the water and sewerage systems will be flowing normally again.

AS IF A sea of sewer water on the loose were not enough, a week after the main broke on Dec. 3 a six-story building in the Bassatine district of the city collapsed, killing 47 residents. Old homes and buildings crumble away here regularly, but seldom does the death toll reach so high.

Then, on the following day, a fire broke out in the Carlton Hotel in the seaside city of Alexandria, burning 10 persons to death and injuring 14 others, including two Romanian tourists. Such fires are a rarity in Egypt.

So far, most Cairenes have shrugged off the bad news and added discomfort of life in Cairo with the phase that has become an Egyptian national reflex toward their daily travails here -- "ma a'lesh," or "never mind."

But outside soothsayers who have been predicting "apocalypse now" for Cairo for years saw in the massive sewerage spill and water shortage the long overdue fulfillment of their prophecy.

After all, they noted, the Cairo sewer system was built in 1914 for a city of less than 1 million and the waterworks dates back to 1865. What else could one expect in a city whose population is now somewhere between 12 million and 14 million?

The infrastructures of Egypt's cities are "virtually disintegrating," said the English-language Egyptian Gazette. "Water networks and sewage systems are in dire need of renovation. What is even more deplorable is that authorities have been aware of such dangers for more than 20 years."

U.S. SPECIALISTS working with the Agency for International Development say the Egyptians actually have already started overhauling the Cairo sewerage network with help from the United States and Britain. AID has obligated $99 million for a rehabilitation project on the west bank, out of a total $500 million it has earmarked for similar repairs nationwide.

Work on putting in new pipes for the sewerage system was close to completion when the big main burst. Water and sewerage authorities were caught in a race against time, replacing old steel pipes with a 10-year life span that were laid down 14 years ago, according to AID specialists.

"The break just beat them to the finish," said one. "Actually, they are doing very well."