Riyadh, Saudi Arabia — Saudi Arabia is beginning to be run by Saudis. Only three years ago, for example, a typical plant supervisor here would have been a foreigner. Nowadays there is a good chance he would be a Saudi.
This ''Saudi-ization'' trend is the latest step in the country's modernization program. Computers, six-lane highways, universities, and shopping centers, paid for with the nation's oil earnings, are now common in this desert kingdom. The know-how, sweat, and materials to build the modern Saudi Arabia came almost entirely from abroad.
The foreign work force, estimated to number about 2.4 million, including approximately 65,000 Americans, has begun to decline, says Minister of Planning Hisham Nazir. Saudi Arabia expects some 70 percent of those workers to leave. Those who stay will fill the lowest-rung jobs or be advisers, teachers, or medical professionals, the minister explains.
''Our short-term problem is not Saudis, but trained Saudis,'' Mr. Nazir explains, adding that the government's development plan for 1985-1990 will emphasize training Saudis for middle-management and maintenance jobs.
To get Saudis into areas vital to the economy, Mr. Nazir says, the government will give more benefits to students who study engineering and medicine, for example, than to those who study history and social science. University admission will be restricted to those with certain qualifications. Others will be steered to new vocational and technical institutes.
But both expatriate and Saudis agree that before ''Saudi-ization'' can become widespread, especially in the private sector, Saudi attitudes have to change.
''Before, it was enough simply to be Saudi. You could be a managing director or a financial director simply by being a Saudi. You had resumes that were very impressive, but you had no skills. You hadn't learned anything,'' says Adel Basri, director of construction for the industrial city of Jubail on the east coast.
The era of foreign firms that hired a Saudi as a front man to attract clients is ending, explains Mr. Basri, who worked his way up. Qualified Saudis are taking jobs away from those who can do nothing more than serve as window dressing. Saudis can no longer make millions by buying a piece of land one day and selling it the next, as in the 1970s, he says.
And Saudis are going to have to work for Saudis because not everyone can be company president, Basri adds.
Diplomats and Western residents of the capital agree with Basri, adding that many Saudis are being forced to apply for jobs they would have snubbed three years ago. This is happening because the government has reduced subsidies on such basics as gasoline and food and because Saudis expect a high standard of living.
Foreign businessmen complain the Saudis are rushing matters, warning that there are not enough competent Saudis yet to take over.
''We'll probably see some horrific problems occur as a result of putting locals into positions prematurely,'' an American businessman says.
A prominent Saudi economic consultant disagrees. ''No one is forcing Saudi-ization,'' says Mahsoun B. Jalal, a founder of the National Industrialization Company. Government organizations have moved more quickly to become Saudi, but sectors such as banking have been more cautious, he says.
''We have engineers now with previous experience, but who are not very qualified yet,'' Mr. Jalal says. ''But we have a good base of them to mix with outside help to get the job done.''
The need for some foreign expertise will not disappear overnight, he cautions. ''You can't find a Saudi with 20 years of experience in petrochemicals or computers.''
But the foreigners say they are departing because the Saudis have made both their professional and personal lives so uncomfortable in many ways:
* Visas for expatriate workers are even harder to obtain than they were two years ago, expatriate businessmen and diplomats agree.
* Very few foreigners coming in now are allowed to bring their families.
* Any foreign firm must subcontract at least 30 percent of its contract to a Saudi firm.
* The government allows a foreign firm very little time to find a new contract after finishing its previous one before the firm is told to leave.
* The Saudis have cracked down on drinking and other violations of Saudi law by foreigners.
Diplomats note that the tougher stand also reflects the growing conservatism of Saudi society and a fear of ''cultural pollution.'' Some businessmen object to what they see as a double standard in applying Saudi laws.