By Selwa "Lucky" Roosevelt

Simon and Schuster. 383 pp. $21.95

For most of us, if we scorch the main course and the dog bites the guests, about the worst that can happen is that they all leave early and never come back.

In diplomatic Washington, such a social mishap could wreck a trade pact or jeopardize our oil supply. The official who takes the rap is the chief of protocol.

Selwa "Lucky" Roosevelt held the job for seven years during the Reagan presidency. She had the rank of ambassador, a car, a driver, a staff and a chance to meet and mingle with kings, queens, prime ministers, ambassadors and assorted spear carriers. It helps if you can afford the clothes. Roosevelt speaks blushingly of the day she almost wore the same Adolfo suit as the First Lady. Only once, to celebrate the signing of the Intermediate Nuclear Forces Treaty, did she wear red, Nancy Reagan's signature color.

Lucky Roosevelt escorted some 350 ambassadors to present their credentials to the president. She attended 70 state dinners. She went to China and to the Moscow summit. She shared a freak tornado, mudslides, floods, high winds and 18-foot waves in California with Queen Elizabeth ("Her glowing skin is a triumph of nature") and Prince Philip ("There are few men in the world more attractive"). She spent 1 1/2 hours in the back of a limousine with Prime Minister Indira Gandhi, stuck in New York traffic (she suggested that Gandhi lean back and take a nap, and she did).

In Roosevelt's book, "Keeper of the Gate," you might expect a feast of tidbits on life backstage with the mighty. But we get a heavy dose of the mighty reacting to the author. They say things like Rajiv Gandhi's "Ambassador Roosevelt, you have not changed at all since I saw you three years ago." (That's when they were stuck for 45 minutes in the National Press Building elevator.)

Roosevelt cites her years covering the diplomatic beat for The Washington Post, when she tried to sneak into Blair House disguised as a member of Jawaharlal Nehru's official party. (She was already too well known. The Secret Service spotted her by name.) She lived in Istanbul, Madrid and London, when her husband, Archibald Roosevelt, grandson of Teddy, was posted there with the CIA.

She met Archie her senior year at Vassar, when she interviewed him for a job. She wore her prettiest outfit, topped by a tiny black hat with a demure veil, and carried her senior thesis, "Communism in the Arab World," under her arm. She thought he was impressed by the thesis. He claimed later he was only being polite. He asked her to lunch, took her to a bookstore and the Metropolitan Museum. The next day he drove her to Poughkeepsie, where they lunched again and hiked along the river and he proposed. Three months later they were married. It was his second marriage and her first, and they lived happily ever after until his death this May.

Lucky -- a name she acquired at Vassar -- was the child of Druze parents from the same small village in Lebanon that produced Ralph Nader's clan. It has since been destroyed in the carnage. Midway through Vassar, she returned to Lebanon to be betrothed to a handsome Druze sheik of her family's choosing. The engagement foundered when the otherwise charming fiance made it clear that as his wife she could never take a job.

Archie, an otherwise quintessential WASP, spoke Arabic, Russian, Kurdish dialects and "all the more prosaic languages." Lucky, an exotic Druze from East Tennessee, knew only a smattering of Arabic, and brought more brass than training to her job.

Certainly there are adventures here one wouldn't want to miss, such as her escorting the ambassador of Swaziland, clad in off-the-shoulder leopard pelts and with bare feet, and carrying a lethally sharpened spear, to see the president. There are also storybook events, like the mile-long buffet at the marriage of the daughter of the king of Morocco, in a vast courtyard where 250 other brides being married the same day were carried about on large trays by ululating tribeswomen. There are conversations like the exchange with the Queen of Thailand, as waiters hobble in on their knees bearing tea and orange juice and gifts wrapped in silk. Out of nowhere the queen remarks: "I have fought the communists all my life, but I cannot fight the menopause."

I like thinking about the King of Morocco's teamakers, setting up their Bunsen burners to brew mint tea for Mrs. Reagan on one of the White House rugs. "We sprang them from the guardhouse," Roosevelt writes, "explaining to the startled Secret Service that these funny-looking guys in pantaloons and stripped vests, red fezzes and pointy bedroom slippers, were part of the King's retinue." There was also an aide in charge of pomegranate juice on that trip, who carried squeezer and pomegranates to all the meetings to slake the royal thirst.

There is much here that adds to our knowledge of diplomacy's quirky ways. The book is a diplomatic rationale for all the Rabelaisian feasting that foreign policy seems to require while the homeless sleep on grates. Roosevelt sees ways that the system could be improved. She feels frustrated that protocol is beginning to be thought of as woman's work.

Yet in the next breath she can exclaim about the "bedroomy eyes" of the Mexican foreign minister or wonder "How could any woman resist" Rajiv Gandhi -- "devastatingly handsome, sensual, powerful, but at the same time tender, sweet, and soft-spoken?"

As the world turns, Rajiv Gandhi has lost his job in India, and Lucky Roosevelt's protocol post is now occupied by a man.

The reviewer is a Washington writer.