Islam -- and limousines -- in Riyadh

The throng of dwarfish Yemenis, garbed in turbans and skirts, who pushed and shoved as they swarmed over suitcases and tips is gone from the Riyadh airport. Passengers arriving in Saudi Arabia's capital no longer run an obstacle course of sleeping humanity spread across the floor waiting for flights to Abha, Khartoum, or Cairo. The jam of battered and dusty taxicabs where drivers leaned on their horns and haggled over fares has vanished, replaced by sleek limousines with fixed rates.

Uniformed policemen speed traffic out onto Airport Road, which is lined with stately palms and even more stately government buildings. This is only the beginning of the utter transformation Saudi Arabia and its capital have undergone in the two years since this reporter was last in the kingdom.

As a new king, Fahd, takes charge of the House of Saud, Saudi Arabia finds itself at a crucial point. It is a point at which the alchemy of development economists has been carried to the maximum. Now it is up to the Saudis themselves to close the final gap between its feudal kingdom of 20 years ago and its present place within that select group of nation-states whose actions directly affect the rest of the world.

Riyadh was the dusty backwater capital of a feudal kingdom as late as the 1960s, when Saudi Arabia struck out in quest of the 20th century. The government's first five-year economic development plan was unveiled in 1970 and committed $9 billion to improving education and health. The second plan turned the rewards of the oil boom into ports, generators, telephones, and roads. By the third development plan, now in its third year, the Saudis had moved on to building industrial complexes and spending more than $236 billion on a dream that is no longer regarded as impossible.

In a remarkably short time Saudi Arabia has achieved the substance as well as the veneer of development.

The signs of change are in every quarter. Traffic, although still death-defying, has gained some semblance of order. No longer are 97 percent of the beds in Sumaizy Hospital, Riyadh's largest general hospital, occupied by accident victims. Saudia, the national airline, is successfully forcing passengers to board airplanes ''wahad y wahad'' (one by one), or the queue, replacing the stampede which was the norm.

The first A&P has opened in the Al Azizia area, with an even newer Safeway down the street. The public scribes who operate out of the alleyway across from the office of the governor of Riyadh have typewriters. Saudi teen-agers hang out at the video arcades.

Saudis no longer hold menial jobs like serving tea or driving trucks. They are merchants, administrators, and bureaucrats. Even the soft-drink vendor who used to work out of a packing crate hut has a new grocery store with wide plate-glass windows. The change has been so fast that it is the norm and not the exception to see an urbanized Bedouin who herded goats 10 years ago now carrying a briefcase.

The building boom continues unchecked. The tall steel cranes that dot the landscape in every direction have been dubbed the national bird of Saudi Arabia. The architectural style and quality of Riyadh's new buildings attest to a maturing of tastes and an appreciation of the aesthetic that was abysmally absent during the heady first days of the oil boom.

The Euromarche, the French K mart, and the expensive shops along Seteen Street have pulled business away from Tamari and Wassir Streets, while the byzantine jungle of shops under the corrugated tin roof that was Deirra has burned to the ground.

The clock tower and ''chop-chop'' square - location of Riyadh's infamous beheadings - are no longer the center of life in the desert capital.

The affluent Saudis are flocking into the new temples of merchandise. The city has become a vast international bazaar. Dior, Cartier, Sony, Panasonic, General Motors, Rolls-Royce, Nike, and Adidas are all there hawking their wares to Saudis and expatriates alike. Many Westerners who were in Saudi Arabia in the mid-'70s actually lament the passing of an era of survival without Spray and Wash, fresh milk, corn-fed beef, sneakers, and electric appliances.

But in fairness to the old days, Riyadh has lost much of its evasive charm. ''Chicken Street'' in Malaaz, location of dozens of vendors roasting chickens over open fires along the street, now has parking meters.

But in the strongest statement of the new generation, the open pen behind the Toyota dealer is gone. No longer are Saudis trading in camels for pickups.

Yet the great consumer society has not breached the wall of a tradition-bound society rooted in fundamental Islam. The process of synthesizing the new with the old has created some bizarre contradictions.

The brightly lighted supermarkets with their wide aisles and imported food sporadically post signs in five languages warning female customers to keep ''all limbs covered'' while on the premises. The matawah, the religious police charged with the ''propagation of virtue and the prevention of vice,'' still ply the streets with camel whips forcing stores to close during the five daily prayer times.

By 1985 the third five-year development plan will spend more than $10 billion building the petrochemical complexes at Jubail and Yanbu and $8 million on a post office education program to teach people how to mail a letter.

It is the confrontation between the material and the spiritual that holds the greatest peril for present-day Saudi Arabia. Keeping the Saudis' bright new world functioning requires the labor of masses of imported workers who are perceived as corrupting Saudi society.