When the phone book lists Western Electric under 'C'

''How does one find the listing for the US Consulate here?'' a foreigner asked the switchboard operator of a Riyadh hotel recently.

''Look under O,'' he replied.

''O?'' the foreigner queried, baffled.

''Yes, for Office.''

Sure enough, there it was: ''Office, American Liaison.''

Five minutes later, the foreigner rang again in search of a listing for the Arabian American Oil Corporation. ''Under C,'' the operator replied with some irritation, ''for Company.''

''Of course,'' replied the foreigner, meaning just the opposite. But sure enough, buried in more than seven pages of companies in Riyadh, Saudi Arabia's capital, was the listing for the world's largest oil company - along with all those other obvious C's: Mitsubishi, Northrop, Philips, and Western Electric.

It became a game, unraveling a ''system'' that was anything but that. Pepsi-Cola was under ''F'' for Factory, while Canada Dry was somewhat more logically under ''C'' - for Company. The Ford Foundation was listed under ''E'' among 12 pages of Establishments, alongside what is indeed a well-known establishment in that barren nation, Desert Road Material.

But it also became educational, for one can learn a great deal about a country from its telephone directories, especially in the Arabian Peninsula, where oil wealth has allowed unprecedented expansion in communications. The Saudi Gazette claims that Saudi Arabia had the fastest growing telecommunications network in the world last year, with a growth rate of 60 percent, compared to an average 6 percent everywhere else.

The growing pains are chronicled in the United Arab Emirates' introductory primer, which instructs: ''To dial, insert the index finger in the finger hole and rotate in a clockwise direction. Hold for four seconds.'' It ends with the useful advice: ''Withdraw the finger.''

The Bahraini directory admonishes beginners on answering technique: ''Do not just say 'hallo' or 'yes,' as this is meaningless and only causes confusion.''

One can also learn about government structure and priorities from a directory. The telephone book for Riyadh includes under Government Ministries the intriguing listing Confidential Information. Could one call for a good gossip, or find out the nitty-gritty on a sheikh, perhaps uncover secret trade figures?

Then there is a listing for Frontiers, and one imagines dialing some lonely guard at an isolated desert post for a chat. Perhaps most reflective of Saudi society was the ominous listing for Discipline & Investigation Board.

One is also left with little doubt that the Gulf states are run by monarchies. Most books in the region have separate sections, usually in pastel colors, marked simply The Sheikhs. An introductory page is followed with complete listings for everyone from the special electrician of a given sheikh to the leader of the palace band.

But one must know something about rank in looking for royalty in the U.A.E. book, for minor sheikhs can be found neither in their own sections nor under their names. They are, of course, under ''S.''

In Saudi Arabia, possession of a telephone is clearly a matter of pride, for everyone seems to be listed, including page after page of the massive royal family, rank noted only by the (Prince) after the name.

Equally Saudi is the fact there are no listings for women, an ironic touch since contact for sequestered females is often limited to the phone.

One can also uncover the economic trends of a Gulf country without leaving a hotel room. The status of oil in Bahrain, where the first Gulf gusher was discovered in 1931, is obviously poor: There are five times more air conditioning and water company listings than oil company outlets. That Bahrain has emerged instead as the commercial center of the region is reflected in six pages worth of banks. They are listed somewhat confusingly under Islamic, Merchant, Offshore, and Specialist.

As with all the Gulf states' directories, to find anything, one must first crack the code.