Rule No. 1 from the luxury hotel managers who collected at the Watergate last night: The more famous the guest, the easier the handling.

"It's only people who are newly arrived," said the Watergate's Nicholas Salgo, meaning economic status as opposed to check-in time, "who are difficult."

An undifficult Houston guest: The duke of Windsor.

"He was really a down-to-earth guy," recalled Gerald de Schrenck Sill of the Warwick in Houston, "not like Wally, his wife. One time the duchess walked in my office and said she wanted to give a dinner for Dr. [Michael] De Bakey. So we went through the whole thing, from the selection of wines to the pheasant under glass, the smoked salmon, caviar, the whole schmiel.

"Then the duke, at about 8 p.m., right before the dinner, pulled me aside and said, 'I know Wally gave you a hard time with this dinner -- but could I have a medium-rare hamburger?'"

Which was just one story of many floating through a cocktail reception room at the Watergate's Terrace Restaurant last night. There, managers in the Preferred Hotels Association sipped wine and politely cackled at the end of a day of meetings about advertising, budgets, toll-free reservation numbers and other things which are different stories entirely.

The association is an exclusive group of privately owned hotels, whose managers get together like this twice a year. Their common ground, they say, is luxury. And judging from a party slide presentation that announced in no casual way that "Preferred Hotels are not for everybody ," these hotels also share a fervent belief in a way of life that has all but vanished except from the very few.

Their attention to detail is painstaking, and, to the casual observer, a bit amusing. Preferred Hotels absolutely have to have bar soap longer than 2 1/2 inches across. There are evening turn-downs of the beds. "A must ," decreed Watergate president Gabor Olah-de-Garab.

And at the Brenner's Park Hotel in Baden-Bden, West Germany, they even poke around in your closet to see if you need any bottons sewed on your shirt. Shine your shoes, too.

Another easy hotel guest: Jimmy Carter.

"At the tail end of the campaign he came to Houston," said Sill of the Warwick. "And I had my chef prepare him something special. When the president came, I asked him if he would like to have dinner, and he said 'No, I just want an apple and to go to bed.'

"The poor chef worked himself to death," sighed Sill. "It was snapper, stuffed with crabmeat and shrimp."

There are 44 hotels in the association -- three in Asia, 15 in Europe and 26 in the United States and Canada. The Embassy Row and the Watergate are the Preferred Hotels in Washinton. There are none in New York. But in Los Angeles, there's the Beverly Wilshire, in Denver the Brown Palace, in Detroit the Pontchartrain, and in Pittsburgh, the William Penn.

Which brings up another hotel guest: opera star Luciano Pavarotti.

"He's standing there in his room," recalled Thomas Lannen of the William Penn, "and I'm talking to him and he looks around and he says, 'Where's the piano?' And I says, 'Piano?' Nobody asked for a piano.'

"And so I call the Steinway people, and they say it'll take two weeks. So then I called Baldwin, and told them what we wanted, and they had it across town and in his room -- in 23 minutes.'"