What did Robert (Bud) McFarlane have in common with Spam, nylon stockings, Bill Cosby, Curious George and the Golden Gate Bridge?

That was easy enough to figure out Sunday night at the Wolf Trap Barns: Like all of them, President Reagan's former national security adviser was celebrating his 50th birthday.

Another question, this one in reference to a presidential memory loss and sung by the Capitol Steps -- What did you do on Aug. 8 of '85? -- required a more tuneful response.

Warbled Vice President George Bush, looking straight at McFarlane seated at the next table: "I met with Ollie North and you."

The audience of about 140 "went nuts," as one of them later described the scene, and led some McFarlane friends and supporters to conclude that more than music was in the air.

It turned out to be a grand night for singing, thanks to the planning by McFarlane's wife Jonda, their children Lauren, Melissa and Scott, and members of his staff. McFarlane, too, exercised the old pipes in a throaty rendition of "immense expense is mainly in defense" (to the tune of "The Rain in Spain"), and even Fawn Hall belted forth a lyrical line.

The celebration started taking shape in May when planners lined up the tunefully topical Capitol Steps to entertain. (They updated their material just five days ago with a new number called "Olliewood.")

The guest list of Cabinet, White House and other folks included Michael and Carolyn Deaver, Malcolm Baldrige, Ken Duberstein, Brent Scowcroft, Paul Nitze, Zbigniew Brzezinski, John Lehman, John Block, Susan Baker and Craig Fuller. One of them, Ed Rowny, the administration's senior arms control adviser, led everybody in the grand finale.

Pulling out his harmonica, Rowny played what you might expect for an ex-Marine turned 50, a chorus of -- "Happy Birthday" and one of "The Marine Corps Hymn."

Just as chronic commuters already know, the New York shuttle is no respecter of Washington's high and mighty -- not even the president's right-hand man.

Returning from a speech to the NAACP in New York Thursday, White House chief of staff Howard Baker was grounded like everybody else so long at LaGuardia that he was last but hardly the least to arrive at Frank and Jayne Ikard's dinner honoring new CIA Director William Webster. (The White House said yesterday that Baker would use a military plane if he were meeting the president somewhere but otherwise prefers to fly commercial flights whenever possible.)

President and Mrs. Reagan were already there, as were others in the handpicked group of 18 that included Attorney General Edwin Meese and Ursula; Marine Commandant P.X. Kelley and Barbara; Sen. John C. Danforth (R-Mo.) and Sally; Sen. Christopher Bond (R-Mo.) and Carolyn ; frequent Webster companion Laurie Firestone, Barbara Bush's social secretary; Nancy Reagan's good friend Mary Jane Wick sans USIA Director Charles Z.; Houston widow Ellen Middleton; and Webster's pal from their Amherst College days, Roger Neuhoff.

Dining that hot night on cold ginger veal, cold salmon, cold green beans and a chocolate raspberry dessert, Reagan was the perfect celebrity guest, leaving the limelight to Webster and the toasting to Ikard.

If conversation about the Iran-contra hearings was politely covert at the three tables, Reagan's reaction to the outpouring of public support for Marine Lt. Col. Oliver North was definitely overt. Even he seemed pleasantly surprised by the amount of positive mail for North arriving at the White House and on the Hill.

Reagan chuckled over a story involving an old friend, comedian George Burns, as told to him by his hostess. At a dinner for 12 Ikard gave a year ago at New York's famed "21" restaurant in honor of the Kelleys, the sky was the limit when it came to ordering. Burns, who also happened to be dining there, couldn't resist asking who the host was. When Frank Ikard admitted that he was, Burns was sympathetic.

"Sir, I really think you deserve a cigar," he said and, characteristically, handed him one.

Like her aunt Nancy Reagan, whose maternal forebears were Virginians, Anne Davis Peterson can now boast of some Old Dominion ties of her own. Married over the weekend to Jon Milton Peterson, Anne is the new daughter-in-law of Milton and Carolyn Peterson of Fairfax, at whose York Harbor, Maine, home the wedding was held. Milton Peterson is the other half of one of Fairfax County's most influential real estate developers, the Hazel-Peterson Companies. With zoning attorney John T. (Til) Hazel, Peterson's other partner on occasion has been millionaire landlord Giuseppe Cecchi.

Credit Jerry Weintraub, chairman of the board and chief executive officer of the Weintraub Entertainment Group, with the idea for a series of movie industry-sponsored antidrug messages being unveiled at the White House today by Nancy Reagan, with Motion Picture Association of America President Jack Valenti.

Funded by MPAA, the project features a major motion picture personality in trailers that will be playing in movie theaters around the country through June 1988.

Mrs. Reagan and Clint Eastwood are together in the first trailer. Others will star Rosanna Arquette, Rae Dawn Chong, Pee-wee Herman, Bette Midler, Dudley Moore, Olivia Newton-John, Roy Scheider, Ally Sheedy and James Wood.

Weintraub's Washington connection isn't just as a Hollywood producer, entrepreneur and promoter. He's a big supporter of the State Department's Americana Rooms and a member of the National Council for the Blair House Restoration Fund.

For the record: Jordan's King Hussein and Queen Noor have agreed to be honorary chairmen of the 1987 Wolf Trap Associates Ball, which will salute Jordan. The ball is scheduled Sept. 11 on the stage of the Filene Center at Wolf Trap Farm Park and the queen is expected to attend ... Former senator Paul Laxalt, whose hat is in the presidential ring, is passing it at his first $1,000-a-ticket Washington fundraiser tonight at the Powerhouse.