The traditional coat of arms of a hotel concierge is a set of crossed keys. Crossed eyes might be more realistic, for a good concierge must function as nursemaid to the rich, secretary to the demanding and confessor to the oppressed. He must produce tickets which are impossible to get, obtain reservations where there are no tables and remember the foibles of the powerful. He must provide joy to the living and help bury the dead.

One of the world's most famous concierges is Michel Rengnez of the Paris Ritz on the elegant Place Vendome. M. Regnez, who started as an elevator operator at the hotel when he was 22, has served the Ritz for 31 years, the last 13 as premier concierge.

When a famous Italian industrialist dispatches a telex advising of his arrival, Michel knows what must be made ready: a half kilo (1.1 pounds) of the best Beluga caviar, a basket of apples and a pitcher of cream.

It is not Michel's to reason why. Just provide the goods.

A retired American ambassador who developed a passion for Charentais melons once dispatched a detailed request for eight of them to be sent to his summer home in Maine. Explicit shipping instructions with designated airlines to be used and customs brokers to be employed were sent off to Michel in Paris.

The responding cable from the concierge's desk was succinct and proper. It read, "Mellons sent July 18, waybill number 8934576929146-K. Respectfully, Michel." Somewhere in a cottage in New England, guests plunged spoons into melons grown in the Charente, trucked to Paris, shipped by Michel at the Ritz, flown across the Atlantic and transhipped to a summer house in Maine.

When famed lioness of fashion Coco Chanel was alive, she stayed often at the Ritz, and being a talkative lady engaged Michel in conversation each night when she returned after dinner. It was not such a conversation as an interrogation. "Mme. Y. from Texas, did she visit Balenciaga? And the Persian princess on the third floor, did she make an appointment at Dior?"

Coco, the irrespressible character about whom a Broadway show was written, was trying to find out through the concierge if her customers were straying to her competitors.

Letter after letter from America lands on Michel's desk with detailed instructions asking for reservations at the famous restaurants. Last summer one from Lake Forest, Ill., went like this: July 7, Taillevent; July 8, La Tour d'Argent; July 9, Grand Vefour, July 10, Lasserre. The bill for such a week of gourmandizing can be enormous. Taillevent is now charging about $70 per person for dinner, without wine.

Michel must stay on agreeable terms with the top restaurants of Paris in order to secure the proper tables at the proper date for the proper people -- and not always with such precise advance notice. The restaurants themselves often give modest cocktail receptions for the best concierges in the city. As much goes for airlines, especially Air France and TWA, which carry most of the hotel's American clients. Fifty-seven percent of the Ritz's customers are Americans.

Among the requests that Michel is asked to fill are those for chiropodists, nurses, and, embarrassingly, for girls. "Tous les gouts sont dans la nature," he says. All tastes exist in nature.

The most difficult and certainly the most memorable request of all came from a Southern banker. He was at the Ritz with his wife and their young daughter and son-in-law who were on their honeymoon. He asked Michel to arrange for one whole railway carriage on Le Train Bleu traveling from Paris to the Riviera. There were only four passengers but the banker wanted all 12 rooms. Moreover, each room was to have a bottle of champagne placed in it.

Michel startled the French railways with the request, but he got it. That rolling bacchanal cost $1,000, plus the champagne.

The word concierge -- which also stands for those formidable women who command the entranceway of French apartment houses -- probably goes back to the 13th century during the reign of Charles the Wise, son of John the Good. When Charles moved into the first part of the Louvre, he transformed his own place into what became the Conciergerie de la Maison du Roi. As Concierge du Roi, the keeper of the King's Household, Charles appointed a general of the army whose duty it was to create a state police force and assume responsibility for security.

The Conciergerie still exists, but its memory has been overshadowed by the bloody events of the French Revolution when the building was used to house those who were to be marched before the Revolutionary Court and then hied off to the guillotine.

Hotel concierges have banded together into an international society of the "Golden Keys," which has over 3,000 members. Within this vast group there is an amicable band who work together and respect each other's feats of magic. A prime list might include such practitioners as Freitag of the Bayerischerof of Munich, Bellini of the Grand in Florence, Burdeyron of the Dorchester in London and Beauharnais of the Pierre in New York.

All of them consider it part of a day's work when a woman guest confesses, as one did to Michel Rengnez, that her husband didn't know how to love her anymore. A paramour was suspected. Could Michel find madame a palmist? "I got one for her, the best in Paris."

Recently the same couple was back at the Ritz. "I saw madame, the other day," he said beaming with satisfaction. "She looked very happy."