She's "Queen Nancy," according to the caption on the American Postcard Co.'s hottest-selling card of the summer season. It shows Nancy-with-the-Reagan-face, and the rest as Queen Elizabeth's, wearing the crown jewels and ermine robe. Somebody mailed one to Time magazine's Hugh Sidey, and just in case he'd forgotten his own words, typed on it: " 'This time around let's have a little class.' Hugh Sidey. Dec. 1980."

Sidey and other First Friends dining at the White House Saturday night just missed a classy Reagan Christmas preview. Ladies' Home Journal produced it for its December issue complete with a picture of Nancy and Ronnie holding a Christmas present in front of an old-fashioned tree in the family dining room. After the picture was snapped, the 12-foot Douglas fir was taken off the life-support watering that had kept it alive for the three weeks before the Reagans got back from their California vacation. And in the shoebox-sized Christmas package?

"I know it's a Cadillac," said the president.

Speaking of "class":

President Reagan told Country & Western singer Rex Allen that every time he wears his new $1,000 Tony Lama cowboy boots inlaid with 14-karat gold presidential seals, "I'm going to keep my legs crossed so everybody can see the tops." Allen says the president's patent leather versions will go "real nice" with a tuxedo so he's hoping to see a little western-style class at some upcoming White House dinners.

Allen and the president are friends from the days when they owned neighboring ranches in Calabasas, Calif. Reagan's spread covered 160 acres, Allen's 18.31 acres. Reagan sold his years ago to 20th Century-Fox. Allen sold his only this March to the Department of the Interior as part of the Santa Monica Mountains National Recreation Area, of which, incidentally, only 1,400 acres have been bought so far -- for $30 million, out of the $36 million Congress earmarked to acquire 55,000 acres. There is still $6 million left, but 53,600 acres to go.

"He hoped I got the right price," says Allen, who thinks he got quite the right price -- at $1.3 million -- after having it on the market a year and a half. (At those prices it's obvious why the government has only been able to afford 1,400 acres so far.) "I don't think Ron believes the government should acquire a hell of a lot more of that land out West. He thinks it should be left in private hands and told me that they're taking a look to see if it's important to acquire any more."

Allen, who doesn't think the government should buy any more land out there either, will next be heard singing the title song in Universal Pictures' "Best Little Whorehouse in Texas."

The sign on Rosalynn Carter's Plains, Ga., office door reads "Nine to noon -- do not disturb" now that she's writing her autobiography, which not even Jimmy is allowed to read. The word is that she signed a contract with Houghton-Mifflin before she left for China, though insiders at the New York publishing house claim it's news to them. Says a Rosalynn confidant: "The only people who know for sure are Rosalynn, Jimmy and God, though not necessarily in that order."

Tourists were disinterested and islanders indifferent to Jackie Onassis' much-ballyhooed summer presence on Martha's Vineyard. Northern Airlines' Steve Voluckas, who arranges aerial tours of that socially tight little island, said people wanting the large overview were more curious about pop singer James Taylor's digs than in Onassis' sprawling new retreat at Gay Head.

Whether by intention or accident, Jackie sightings were usually on weekends. She might claim she wasn't antisocial, just helplessly incommunicado, thanks to the U.S. Postal Service. Washington literary agent Audrey Adler Wolfe picked up the phone the morning after a dinner party she and her husband Billy had given in Edgartown for Doubleday's senior consulting editor, Ken McCormick, to hear an apologetic voice explaining why she hadn't RSVP'd. It was Onassis, a colleague of the highly respected 75-year-old McCormick, complaining about mail delivery, like everybody else these days.

Among the Wolfes' guests who did get their invitations were retired Vineyard Gazette editor Henry Beetle Hough, 85; Helen Cronkite, 89, and Audrey's ex-mother-in-law Louise Adler, 78, who all reminisced about the good old days when there really were grapes in the Vineyard.

There are going to be more -- at least white grapes -- on the Vineyard, if Lady Bird Johnson has anything to do about it. Up to her old (the green-thumb-is-quicker-than-the eye) tricks, she planted a grapevine in front of Charles Guggenheim's Vineyard Haven home -- borrowed by Liz Carpenter and the Harry Middletons for a couple of fast-paced weeks of margarita tasting, poetry reading, nature walking and wedding watching (Prince Charles and Lady Di, courtesy of Art and Ann Buchwald who tossed a 5 a.m. omelette party and gave out tiaras and crowns as favors). After the planting ceremony, Rose and Bill Styron, John Marquand, John Hershey, Walter and Betsy Cronkite, Lillian Hellman, Libby and Doug Cater and Edith and Henry Beetle Hough polished off 11 dozen tamales flown in from Texas..

Jayne and Frank Ikard's latest whaling and dealing real estate coup involves cashing in their two houses at the Vineyard to buy a third, all in one wild 24-hour period. When Jayne's all-time favorite Edgartown house, supposedly part of an original whaling ship, came on the market, she launched into her best sales pitch to hawk her house at Chilmark and their house at Edgartown. Then she skipped town before local real estate agents could heat up the tar and feathers over their lost percentages.

Ursula Meese came home from her Middle East inspection trip to find that "President" Edwin Meese had borrowed yet another hat in her absence, the one she's been wearing for the Multiple Sclerosis Society as head of its Sept. 22 Ambassador's Ball. "Chairman" Ed netted $25,000 for the event merely by plugging it over lunch at the exclusive all-male watering hole for 50 top Washington lobbyists called the Carlton Club. ("We don't have anything against women members," says prexy Edwin M. Wheeler of the Fertilizer Association. "It's just that none has ever been proposed.")

Even at $5,000 a crack, 10 percent of the membership couldn't sign on fast enough as ball "benefactors," which means they will get to have dinner with OAS Secretary General Alejandro Orfila the night before the ball. The next night, along with 1,000 others, they will dine with corporate America's two favorite "chairmen" of the board, President Reagan and Frank Sinatra, who just happens to be head of the MS national fund drive.