When Jacqueline Kennedy Onassis tells friends that her architect has brought her new house on Martha's Vineyard in "under budget," she means under $1 million.

And only about $5,000 under, at that. By the time she adds architectural fees and other incidentals the construction cost is being figured by those who know at $995,000.

The 356 acres of ocean-front land cost her another $1 million, and just recently she picked up a small adjacent parcel to round out her boundaries for $15,000.

She has been flying into the country airport frequently on the Paul Mellons' blue-and-white Gulfstream II to oversee the start of construction.

Last week, she and her super-rich friend Bunny Mellon -- who has been helping her on the house's perfectionist details -- stepped off the luxurious private jet into a waiting pickup truck and were whisked away.

The Onassis house is remote, with a long, long private access road. Trespassers are going to need wheels or jogger's shoes and a lot of running experience to huff and puff their way close enough to see anything.

Local pilots of small craft-for-hire are already being booked by photographers who want to fly over for an aerial shot once there is enough of the structure underway.

The house will be the most expensive Onassis has ever owned. If it's any consolation, the place is already worth more than she paid for it. According to local real-estate agents, her presence there has pushed up prices around her.

Now that he has been cleared of cocaine-sniffing allegations, White House chief of staff Hamilton Jordan is apparently not going to be as reclusive as he was for a while. At 1 a.m. on a recent Saturday, he was sitting at a sidewalk cafe with a beautiful blond, sipping a drink and trying to look as anonymous and inconspicuous as possible. . .

As an international lawyer, R. Sargent Shriver may not have much courtroom experience.But he sounded like Melvin Belli in traffic adjudication court recently after his car was towed away downtown. He succeeded in getting his $50 tow fee dismissed but still had to pay a $10 fine. . .

Despite entreaties from friends and associates, Henry Kissinger is refusing to be interviewed by investigative reporter Seymour Hersh for the unauthorized biography to which the former New York Timesman is devoting a couple years of his life. Former Kissinger aides are also sending Hersh what amounts to a form letter, saying they don't want to talk, either. Hersh, meanwhile, has been flying all over the world to places like Hanoi and says he doesn't blame Kissinger for "getting nervous." Sounding like the old radio voice of "The Shadow," he says gleefully: "Who knooows what they showed me . . . who knooows what documents I have seen . . . who knooows what secrets lurk in the hearts of men" . . .

When Maryland's Marvin Mandel divorced his first wife, "Bootsie," and forced her to vacate the governor's mansion, his fortunes were up and hers were down. Now, in one of life's ironic little teeter-totters, comes this vignette that is enough to make ex-wives everywhere smile. The week that Mandel went off to prison, an old friend ran into Bootsie Mandel, looking terrific, expensively coiffed and costumed, and having a $200 dinner at the Four Seasons with a new beau . . .

London hostess Fleur Cowles, who founded Flair magazine, was telling friends at a dinner in Los Angeles about her newest hobby. She collects castles in Spain and has just bought a 9th-century castle to go with her 14th-century castle and her 11th-century castle . . .

White House counsel Lloyd Cutler says that he was asked recently to help with federal judicial appointments and had a moment of temptation when he thought of his daughter, who is a judge in Alaska. "Just for an instant," he says, "I thought of writing her name in [for a promotion] and hoping nobody ever caught on."