A Saudi business leader assesses the economic climate of his country

Most of Suleiman Olayan's investments are privately held and thus not subject to any disclosure rules. But his net worth, an assistant says, is often put at ''above $100 million.''

That's probably super modest. Considering the extent of his holdings, he could well be one of the richest men in the world.

Inside Saudi Arabia, the Olayan Financing Company alone is involved in 44 joint ventures and subsidiary companies in a diversified mix of light industry, agricultural services, and high-technology industries. And the Olayan Group of Companies is divided into six more entities. One holds a number of trading, contracting, and transportation entities. Another manages a portfolio of Saudi public securities, such as those of banks and cement companies. A third manages the group's real estate holdings in the kingdom; a fourth the group's international investments. These, it is reported, include a 7.5 percent share of First National Bank of Chicago, one of the larger banks in the United States as well as ''around 1 percent'' of Chase Manhattan, Mellon Bank, Bankers Trust, and some other sizable American banks.

Then there is Arab Commercial Enterprises, the largest insurance and reinsurance concern in the Middle East; and another company holding long-range investments, such as buildings, outside of Saudi Arabia.

A four-page biographical background also lists board memberships (such as Mobil), club memberships, and other activities (including current chairmanship of the Riyadh Chamber of Commerce and Industry, an underwriting member of Lloyd's of London, and affiliations with various think tanks). William E. Simon, a former secretary of the Treasury, helps him from New York with his investments.

In other words, Mr. Olayan is not a business-naive Bedouin fresh from the desert; he a sophisticated, international businessman with a strong base in his homeland.

In an interview, looking at the Saudi Arabian economic scene, he pointed to several trends:

1. Saudi customers have become more demanding in the quality of goods, services, and accommodations they acquire.

2. Considerable speculation has blown out of the Saudi real estate market. Businessmen are buying only the land they need for expansion; not extra land for speculation.

But building rents have not come down ''as much as they should.''

3. Business has slowed somewhat because so much infrastructure - roads, ports , airports, telecommunications, etc. - has been completed.

Mr. Olayan believes that entrepreneurship is an ''indigenous characteristic of the Saudi'' - a people who before the discovery of oil depended on importing or trade, on agriculture, and on catering to the hajj pilgrims.

Because so much of the new oil money was spent on construction, the early Saudi entrepreneurs were busy supplying concrete, equipment, contracting, or other such activities. Indeed, that is how Mr. Olayan got his start in 1947 - acting as a contractor of his former employer, Aramco.

Domestic cement production grew rapidly from almost nothing to 10 million tons a year, compared with consumption of about 15 million tons. That compares with production in Egypt of 4.5 million tons.

''That shows you how quickly the private sector, with government encouragement, has taken on itself to provide the country's needs,'' he said.

Now Saudi businessmen are becoming more specialized, launching light industries.

Saudis, he adds, are individualistic. ''That is how we survived hundreds of years in this harsh environment.''

He emphasizes a need for greater education and training of Saudis so that fewer foreign workers will be needed. ''I am not saying we will ever be without a foreign labor force, especially technical, clerical, and management. I think it is more true now - there is one world and there will be interdependence.''

So far, Saudi Arabia's top businesmen, like Mr. Olayan or the Juffali brothers, have largely kept their companies tightly held family concerns. Stock of relatively few companies, such as some cement companies and banks, have been sold to the public. But they usually remain under the control of a minority partner.