THERE WERE bound to be surprises. Like the falcons flying in first class.

"On the Saudi airlines, they keep the birds up there on sticks that look like giant golf tees," says Robert Lacey, author of the new history, "The Kingdom: Arabia & the House of Saud."

Or the deluge of scents. " 'The perfumes of Araby' is not an empty cliche'," he says. After a dinner with the male gentry, "the servants would bring in great flasks like milk bottles full of Chanel and 4711 and the men would sort of rinse their hands in it."

Or the incredible heat. At 120 degrees, says his wife, Sandi, who lived with her husband for 18 months in the desert nation, "I'd have to get up at 6 a.m. to do the laundry--just to get water cool enough so that the colors wouldn't run."

In semi-repose in the Jefferson Hotel, the British pair look spiffing and chipper as up-scale honeymooners. But there are latent tremors of Saudi-shock as they pound the promotional pavement in the hopes that the 38-year-old author's chronicle of the Arabian dynasty from 1900 to the present can match the success of his 1977 best seller, "Majesty," about Queen Elizabeth and the House of Windsor. After all, he says, the House of Saud "has power that makes even the Rockefellers look insignificant."

Educated at Cambridge, he spent his holidays working as a tour director for groups of young women traveling in Europe. (Differences in dialect were problematic: Some American girls were once horrified when he announced, "I'll be coming around in the morning to knock each of you up.") "But my history tutor suggested politely that perhaps I wasn't quite suited" to academe, recommending the MI5 intelligence service. Lacey joined and might have stayed, had it not been for an essay contest in the London Sunday Times offering the winner a round-trip ticket anywhere in the world.

Lacey had fallen in love with a South African girl in one of his tour groups, and entered the contest to visit her. He placed second, winning 80, enough for a ticket. The romance came to nothing, but the article got Lacey his next job as a feature writer at the Times. By then he had married Sandi and worked from 6 to 9 each morning on his early biographies of Robert, Earl of Essex, Sir Walter Raleigh and Henry VIII. "They got wonderful reviews, sold no copies at all," and he paid his own way to the States to promote them. But when Sandi suggested "something on the British royal family," the result, timed to coincide with the Jubilee Year, left him with nearly half-a-million dollars and a professional quandary.

"My British publishers wanted a sort of 'Son of Majesty,' about Prince Charles, but my American publishers wanted a book about the American royal family, the Kennedys." The Kennedys prevailed, and in 1977 the Laceys started looking for houses in Chevy Chase. But then one day Lacey was talking to a Palestinian woman who "told me a story I had never heard," about how Abdul Aziz (1876-1953), known in the West as Ibn Saud and the patriarch of the royal line, had set out with a handful of Bedouin raiders to unify Arabia in the first decades of this century. He was excited. Sandi, a graphic designer, was not: "It was a nightmare," she says, that "nearly caused the breakdown of our marriage."

"The Saudis are a cautious people," says Lacey, "and I realized that the only way to get any kind of trust would be to take my family and go there to live." And he had fortunately "met a family of Saudi merchants who were willing to take the risk of signing my entry papers. The only way you can get a residence visa in Saudi Arabia is to find a Saudi who will take the blame for you, who puts his name to all your documents, who keeps your passport in his safe and to whom you have to go when you want to leave the country to apply for an exit visa." Although Lacey paid for these services, he is grateful to his sponsor for "risking his good name on the project."

Once committed to the residence, Lacey was not wholly candid about his plans: "You told me three months, darling," says Sandi, who suspected the worst during a vacation in Crete when Lacey opened his suitcase and a Koran fell out. By 1978, they were in Jeddah.

More practiced travelers would scarcely have quailed at the Islamic rituals and indigenous customs of Saudi culture. And Lacey, who had spent months on a crash course in Arabic and had made a preliminary trip to Riyadh, was somewhat prepared. But his wife was not. "It's like landing on the moon," she says, recalling the perpetual lung-clogging nimbus of dust and sand. Not to mention: the strip search at the airport by women in heavy veils ("It's terrifying if you can't see their faces"); the small house they rented ("the power would go on and off without warning"); the exotic dinners ("hundreds of dishes" including roast goat); the virtual imprisonment at home with their daughter, Scarlett, then 6. (A son, Sasha, now 15, stayed in England at school.) "Women cannot drive, so there I was with the car outside and the keys in my pocket, but I couldn't get out!"

As the stay stretched to nearly two years, Lacey expended not only the $200,000 advance from Harcourt Brace Jovanovich and the 50,000 from his British publisher, but much of his savings and a sizable portion of his spouse's good will. There was much to adjust to. Movies are prohibited, Lacey says, "because people of the opposite sex could meet under cover of darkness," but television is encouraged as "good family entertainment," which includes "the Arab soap operas, made in Egypt. There is much shouting and weeping, and when somebody gets killed, there's blood all over the place. It's great!"

Sandi was at first shocked by the universal segregation of sexes. The several hundred women doctors treat only female patients; the women's banks serve only female clients. At public beaches, women appear fully clothed, wearing veils; and just before the Laceys arrived, public swimming pools had been closed to women: "Apparently two Western stewardesses had taken their bikini tops off"--monstrously appalling in a land where showing hair is considered seductive and where "whole blocks of flats remain unoccupied," Lacey says, "because they were designed on the Western format, with only one living room instead of two--one for men, one for women."

But Sandi found "a great sense of sisterhood" and had "some fantastic times." One was her attendance at a royal wedding party (half of it, anyway: the men's side met across town at a different time) where after getting off at the wrong floor and scandalizing the hotel by appearing in public with her face and arms uncovered, she located her group--scores of women with their hair swinging free, listening to an all-female band and wearing "the most wonderful Western dresses." Lacey says that in the present Spenglerian gloom of the Western economy, only the wealthy Saudi women "are keeping the tradition of individually made haute couture garments alive." But the elegant ladies wore "proper spectacles" because contact lenses are considered a sign of vanity. And a visit to the ladies' room uncovered "a whole room full of women smoking, gasping." Lacey says, "The Saudis of our generation don't smoke in front of their parents. I once saw a Saudi stub a cigarette out in his own hand at the news that Dad had arrived."

The author had his own set of "firsts," including "the first time I had eaten with my hands, the first time I ever played party games at an adult gathering, and the first time I ever took Valium"--for a mental and physical collapse brought on by his work. Among Saudi officials, Lacey says, "the standard technique is that they never say 'No.' They say, 'Come back next week.' This utterly defeats the average traveling correspondent." Then there was censorship. Many source materials had to be smuggled in with the help of his research assistant in London (when she arrived for a visit, Lacey's driver asked if she was "wife number two"); and even the International Herald Tribune would be censored if it contained a story about the Saudis, so Lacey arranged to have the offending headlines cut out in advance and sent to him separately.

Lacey's sponsor introduced him to many members of the royal family, and he cultivated the acquaintance of some young princes who had been educated in America, parlaying one contact into another, gaining interviews with religious and business leaders, making forays into desert camps, socializing with the younger royalty, even dining once with the king. ("So what?" said an unimpressed bus driver. "The bedouin go and sit with him every day.") The briskly paced history leans heavily on scholarship, including nearly 100 pages of appendices, bibliography and notes. But there are many contemporary vignettes, such as King Khalid hunting with his falcons. He travels in a Range Rover with the top sawed off and filled with "huge, plush sofas on which the royal party bounce off towards the hills.

"When they see the game, a button is pushed and King Khalid's armchair rises into the air," allowing him to release the birds. On the way back, "if the hunting has been good, King Khalid picks up the microphone of the walkie-talkie in his dashboard. Into it he sings the verse of a victory chant sung from time immemorial by bedouin returning from a successful raid . . ."

And there are vivid, gossipy anecdotes from the history of the kingdom. Item: During the negotiations for the original 1933 agreement with Standard Oil of California, a lease agreement on resources which by 1981 would be worth a net revenue of $315 million per day, Abdul Aziz dozed off. He doubted that there was really oil under the sand, and felt he was simply "getting 50,000 in gold for nothing."

Item: In 1946, Winston Churchill gifted the patriarch with a magnificent Rolls-Royce limousine, specially equipped with silver fittings and with its rear seat custom-converted to "one huge armchair . . . to accommodate the generously proportioned royal stern." Abdul Aziz was not impressed. "Only women sat in the back of cars," and the right-hand drive meant that the king would have to sit to the left of his driver, "the position of dishonor." He gave the car to his brother on the spot.

Although his book has been banned in Saudi Arabia--"it did wonders for sales in London"--and despite his difficulty adjusting to the all-encompassing religiosity of "people who believe that reading the Koran can help you fly a fighter plane better," Lacey emerged with a positive overview of the nation that has one-fourth of the globe's oil, where barefoot nomads consort with royalty but slavery was not abolished until 1962, where stupendous wealth coexists with Koranic injunctions to austerity. "It doesn't attack religion--it validates it. They believe they wouldn't be wealthy if they weren't religious, so they feel no guilt, no shame."

Many worry that the Saudi regime may be susceptible to an Iran-style revolution, but Lacey is bullish, "because there is no gap between the rulers and the people. Ordinary Saudis can sit down and talk to the equivalents of Alexander Haig or Caspar Weinberger"; and oil income means that "no Saudi lacks for anything he wants, and if money can put things right, it does."

Moreover, the internal dissension that has plagued the house (notably the bitter feud that led to the ouster of King Saud in 1964, which Lacey calls the "Saudi Watergate") only shows the "great sense of preservation" in the family; and most external threats dissolve because "the Arabs are capable of feuding bitterly and then embracing as blood brothers." Still, the Saudis dread violent extremists like those who attacked the mosque at Mecca in 1979. "Life would be perfect if it weren't for the Palestinian-Israeli conflict. They fear most of all the Palestinians--and the Arab Palestinians are considered just as bad as the Jewish ones."

Lacey may take up this subject in his next book, for which he plans to live in Israel. Sandi wants to move to New York or Washington, but seems nearly resigned. "When he came back from Saudi Arabia, he was muttering about Lebanon! So I suppose Israel is an improvement on that."

But for the time being, Lacey says, "I've had one incredibly broadening experience. I need a lot of rest before the next one." He won't be getting it soon. After a quick talk with People magazine on the phone, and a discussion with an HBJ official about doing the "Merv Griffin Show," the Laceys are off for engagements at the National Press Club and many points west.

"The Arabs have a saying," Robert Lacey says: "You Westerners are the slaves of time--and we are the masters."