Nabih Baeshin, a biology professor at King Abdel Aziz University, stood in the dusty ruins of Jeddah's old city -- a maze of crumbling coral limestone, three- and four-story buildings still holding on precariously to the fading lattice-work beauty of their rawashin bay windows.

"It is too expensive to repair and keep them up," Baeshin remarked ruefully, pointing to the house where he was born but which now stands abandoned and learning, Pisa-like, over the narrow dirt street running through Mazloom district. "People have moved out to the new villas. They have become Westernized."

Once the thriving center of Jeddah, Mazloom today is the decaying living quarters of mostly transient Yemeni workers, a slum of history 200- to 300-year-old townhouses built in Ottoman times out of the spungy coralstone taken from the harbor and originally held together with the slime and mud taken from 40-Meter Lake lying just behind it.

The mayor of Jeddah, Mohammed Farsi, has begun a belated rescue operation, the first anywhere in the kingdom, to preserve the fast vanishing monuments of its architectural history. A survey has identified about 600 old homes for preservation but half are in a such disrepair they may not be salvageable.

Farsi, who runs Jeddah a bit in the style of Chicago's late Mayor Daley, has tried to get the city's rich merchant families to buy and restore the best of the old homes but so far has persuaded only 15 or 20 to do so. The city has bought a few of the most famous and turned them into museums.

Meanwhile, bulldozers continue to bring down another row of old homes along the western edge of Mazloom, just across the street from Jeddah's main covered marketplace, dominated by a 25-floor skyscraper totally out of keeping with the character of the old city.

For a kingdom so deeply attached to its Islamic heritage, the near total destruction of its architectural patrimony -- including what is reputed to have been Eve's tomb in Jeddah -- seems strangely out of character. Yet the Saudi head-over-heels tumble into 20th century modernity has taken a devastrating toll. It has also created an abundance of anamolies, and some admitted architectural horrors, of which Farsi and a few others are well aware.

They blame it on foreigners, Egyptian and Syrian urban planners, and their books note that an American construction company began the activity here in 1947, taking down the old wall of Jeddah, which dated back to Persian times, to provide landfill for the city's expansion.

An example of such horrors is Jeddah Towers, the city's first experiment in "rush housing" and high-rise living.

Across town from Mazloom by the old airport, the $600 million complex of 32 15-story buildings seems the latest word in apartment living and is light years aways from Saudi tent-and-camel Bedouin traditions. Each apartment has three bedrooms and bathrooms, a living room, dining room, kitchen and several balconies, with wall-to-wall carpeting and central air conditioning.

But there is only one elevator in each building and rigid Saudi custom insists women use a separate one. So the complex has stood empty for a year awaiting construction of more elevators.

Farsi, in an interview, said the Towers, whose high-rise style he deplores, will be occupied this summer by 2,000 "low-income" families from a slum area earmarked for bulldozing.

Low income, however, is relative. In Saudi Arabia, the per capita income is $17,000. So Towers residents will be paying $600 a month in installments toward final ownership of their fancy apartments in 25 years.

Just how this experiment in the Westernization of the Saudi living style is going to work is the subject of much debate among city planners, and apparently prospective residents of the Towers as well. Farsi has been holding meetings to "allay their fears," one local newspaper said.

Not all the new architecture is bad. Scattered around Jeddah are fascinating sculptures, some made of metal piece from the city's first desalinization plant, and the new King Abdel Aziz Airport opening in April is, as Brig. Gen. Said Amin, the director, put it, "unique in the kingdom and maybe the world."

Its focal point is the breathtaking terminal designed by Skidmore, Owings and Merrill, being built to handle 80.000 Moslem pilgrims a day, a largely open-air pavillion covered by teflon-coated fiberglass tents held aloft on 10-story pillars.

An aura of fleeting time is reflected in the rush to build a new industrial society overnight, just as it is in the sense of a race to beat the population explosion here in Jeddah. Historically the gateway to the holy city of Mecca, Jeddah has grown from 30,000 in 1947 and 325,000 nine years ago to almost 1.4 million today. More than half of its residents are foreigners.

The urban sprawl cover 155 square miles and stretches almost 20 miles to the north and 15 miles to the south, with satellite cities springing up on the fringes. The city has built 2,500 miles of new four- and six-lane highways and overpasses to handle the 630,000 cars registered here.

Mayor Farsi spends his day running around the city to oversee the many slum clearance, road building and beautification projects. His pet one is the new corniche, a 35-mile stretch of landscaped roadway, public gardens, restaurants, beaches and modernistic sculpture that will eventually, he says, include a park, zoo, museum and an artifical island connected by a causeway to the mainland.

"This has changed everything," Farsi says with pride, explaining how the corniche is being used to "turn the city around" to face the sea rather than the faraway Hejaz Mountains.

Asked why the building frenzy, Farsi replied, "Time is very important. We calculate by hours and minutes . . . We like people to see how the city is changing every minute of every week. I don't want people to think there is no change."

His deputy and city engineer, Hamza Amer, explains it another way.

"If you don't do it today, you will pay double the price tomorrow. If you have the money, the plan and time, you say you must do it. Also there is a real demand from the people, and if you don't build the houses, they go ahead and build on their own but not with good standards. If you don't put up the skeleton of the city now, when will it be done?"

Farsi estimates that the population here will reach 2 million in five years and that Jeddah will then be more a metropolitan area than just a city. "You just cannot stop people from coming," he says with an sigh of resignation. CAPTION: Picture, Jeddah Towers, a $600 million apartment complex of 32 buildings, stands empty until separate elevators for women are built according to Saudi custom overlooked by builders. The Washington Post