The Really Royal Reagan treatment for a visiting head of state is when the president's "kitchen cabinet" has been asked to roll out the red carpet, as some members of it were for King Hussein Friday night. They did it at Chasen's, the "in" Beverly Hills restaurant where the Reagans love to dine.

"It all came up rather suddenly, but I expect we'll be doing it again," said Bonita Granville Wrather. Chief of Protocol Lee Annenberg sent a quick signal to the western branch of the Reagan elite after it became apparent that Hussein wanted to meet those Reagan insiders who helped put him in the White House.

"You're going to be with all my close friends. I wish I could be with you," the president told Hussein on his way out of town.

Saturday night there was more glitter, only this time Jerry and Betty Ford were dinner hosts at The Bistro, another favorite Reagan hangout. Their guest list included Bob Hope, Larry (J.R.) Hagman, Debby Boone, Armand Hammer, Cary Grant and nearly 60 other glitteries whose names may not be household words but whose companies -- American Express, 20th Century-Fox, Rockwell International, Northrop Aviation, to name a few -- sure are.

Great thoughts of great men. Ever wonder what heavy pronouncements and incredible insights are passing between those famous faces of the front pages when photographers catch them in a heart-to-heart?

The Saudi peace plan, perhaps? F15s? Russian shopping lists?

Eavesdrop on George Bush and King Hussein as they descend the marble staircase at the Renwick Gallery.

"I thought Bill Macomber looked skinny," Bush told Hussein the other night. "I think he's lost a little weight."

Some of those lost pounds may have been acquired back in the early 1960s when William B. Macomber was ambassador to Jordan. He is now president of the Metropolitan Museum of Art. But Macomber, when told of the Bush remark, hopes George is right.

Next eavesdrop on Bootsie Galbraith, whose husband, Evan, is the new U.S. ambassador to France. It was during one of those toe-squinching lulls in conversation when even presidents are at a loss for what to say next -- in this case, French-speaking Franc,ois Mitterrand and English-speaking Ronald Reagan.

"I have a question of state to ask, Mr. President," the quick-thinking Bootsie told President Reagan at the shipboard luncheon Mitterrand gave for Reagan in Yorktown. "Would you suggest I introduce myself in France as Marie Helene or as Bootsie?"

If it gave "Dutch" Reagan pause, at least one guest, Jacques Cousteau, always the urbane Frenchman, had a diplomatic solution.

"Why don't you be Marie Helene for the first hour?" he suggested as everybody laughed and began to relax.

And while we're eavesdropping, why not listen to millionaire art collector David Lloyd Kreeger as he stood contemplating a portrait of his hostess, Jayne Ikard, at a brunch she and her husband, Frank, gave.

"I've had three portraits painted of myself and never liked any of them -- at first. But after a few years when I got older I always liked them better," Kreeger said.

"Well, I call my portrait 'Frank's Wife' because everything you see of me there Frank endowed me with," Jayne said of her provocative likeness swathed in pearls, fur and a low-cut green velvet gown.

"Not everything, my dear," Kreeger assured her. "Obviously you were endowed with some things already."

"One of these days we'll all wake up to discover that the only ambassador left in town that anyone knows is Willy Wachmeister."

That assessment by one Washington socialite may be something of an overstatement, although Sweden's Count Wilhelm Wachmeister has inched up another notch to No. 8 in the official order of diplomatic precedence (he's been here since June, 1974), with the departure this month of Tunisia's Ali Hedda.

The Embassy Row exodus next will include Austria's Karl Herbert Schober, Canada's Peter Milburn Towe, France's Franc,ois de Laboulaye, Cameroon's Benoit Bindzi and Greece's John A. Tzounis. (A spokesman for the No. 2 man in the diplomatic corps here, Timothee N'Guetta Ahoua, denies rumors that he is returning home to become a key aide to the president of the Ivory Coast.)

Schober, de Laboulaye and Tzounis are all retiring from the diplomatic service; Bindzi will be ambassador to London; Hedda's new position hasn't yet been announced, and Towe will head Petro Canada International, the subsidiary of a crown corporation involved in oil exploration.

Elections in Greece that brought the socialist government of Andreas Papandreou to power cut short John Tzounis' stay, though not that of his wife, Helen. She's rented a furnished house and intends to remain until June when their son, Constantine, l8, finishes school. Worried that her continued presence on the Embassy Row circuit might prove confusing (her husband's successor, incidentally, is a bachelor) she says she's going into "hiding" for a while.

He is "Mr. White House" to most people around the Executive Mansion, though in the November issue of House & Garden John Ficklin sports a brand new title:"sommelier." Not so, says Nancy Reagan's press secretary, Sheila Tate, of the man who has been a distinguished member of the White House staff for nearly 30 years. "He's still the mai tre d'ho tel. He hasn't been demoted."

Metal detecting Tout Washington at the opening of "La Bohe me" Saturday night was straight out of "Airplane" as grandes dames indignantly bared their gold evening bags to reveal no bombs but lots of lace hankies, and at least one very pregnant opera-lover told security officers she'd prefer to be frisked.

One look at the presidential box told everybody why. There, with Beverly Sills and the Roger Stevenses, stood President and Mrs. Reagan. When the orchestra struck up the National Anthem, all except the Stevenses belted it out like troupers.

"I don't sing anything," Stevens said later. "I haven't sung a note in 25 years."