Invariably, it is the first question they ask: Are you a Blair Blair?

Yes, Edith Blair is really a Blair Blair, a member of that ancient Washington family immortalized in bronze plaques and history books and oil. It is a family that loaned money to a president, shaped the course of a war and gave a name to Blair House, Jimmy Carter's across-the-street place for his out-of-town guests.

The Blair Blair question is a perpetual one that visiting heads of state or Secret Service agents ask when they're # greeted at the house by the slender, wispy-haired assistant manager who calls herself Miss Blair. All those people on the walls, they say, couldn't belong to you.

Sure they do. There's Uncle Gist over there, Uncle Gist as in Gist Blair, friend of William Howard Taft. And on that wall there is Great-great-grandfather Francis Preston Blair, editor of the old Globe newspaper that was to become the Congressional Record. And And don't forget Great-grandfather Montgomery Blair, post-master general under Abraham Lincoln.

Edith Blair's introductions to the family portraits are chatty and breezy, in tones others use to introduce Cousin Marthas or Aunt Beths as they appear in ceaseless family slides of Labor Day picnics.

But Blair shrugs off the painted blue bloods. "We had grown up knowing that the family was important in the 1800s, but in school, a Blair wasn't any more important than an Eisenhower or a Truman," she remembers. "Sure, we were old D.C. society, but being a Blair Blair didn't stand out at all."

As a former teacher and medical assistant, Blair, 39, applied for the $13,000-a-year job just like anybody else. That was last May and by June 19, 1978, she had a new office in a small basement room at 1651 Pennsylvania Ave. NW. She had wanted it for five years.

There hadn't been an opening until Peg Murray, the former assistant manager, resigned and even then, Blair says she wasn't completely convinced the State Department would think her a natural for the job.

"I'm a Republican in a Democratic administration and they could have turned me away just like anybody else," she says. But after all, Edith Blair is still a Blair Blair and turning her away would seem like turning her away from her own home.

It never was her own home, actually, although Blair still remembers it as the home of Uncle Gist. And even though she was only 2 when Gist Blair sold it to the government for use as a guest house in 1942, the home was always part of the family. She visited it while she was growing up on Kalorama Road, and her dad, the third of the three Montgomery Blairs, used to tell old stories about the house as the spirit moved him.

Like the time during the Eisenhower administration when visiting foreigners (Blair won't say who) skewered a lamb and roasted it over the fireplace in one of the upstairs bedrooms. The meal was simmering along just fine until the rug began to flame. Because of that, the use of all Blair House fireplaces has been banned.

Then there's the story that one of the butlers likes to tell about Cora, a maid who died in the house. Her ghost haunts the old rooms and closets, it is said.

And in 1950, the house was the site of an assassination attempt on Harry Truman, who was living there while the White House underwent renovation. Truman was inside napping and wasn't injured, but a police officer and one of the Puerto Rican nationalists who made the attempt died in an exchange of gunfire.

Blair, who was 10 at the time, remembers it well. "We were very much aware that Truman had been shot at in the house. It made a lasting impression on me."

These days, Edith Blair can add a few stories of her own to the legends. After all, she was hostess to Chinese Vice Premier Deng Xiaoping in January, Israeli Prime Minister Menachem Begin in March and Japanese Prime Minister Masayoshi Ohira in April and May. An Egyptian-Israeli peace treaty and a dramatic U.S. visit from a once-hostile Communist country are now history and Edith Blair feels that once again, like the rest of her family, she is too.

Of course, living history as assistant manager of Blair House is not quite the same as living history like those great greats of hers did. Her ancestors advised a troubled Abraham Lincoln about the Civil War and loaned $10,000 to a financially strapped Andrew Jackson, but in 1979, Edith Blair advises food distributors about menus and lends moral support to a house staff in the before-a-state-visit frenzy.

There are plenty of historical tidbits, though. How many others have access to King Hussein of Jordan's eating habits? (He likes hamburgers, medium well with the works, according to the house cook.) Or Deng Xiaoping's favorite American food? (Veal, but if the truth be known, he'll eat anything.) Or details of Menachem Begin's kosher diet? (Fish constantly.)

"We're America's number one hotel," says Blair, "but we're trying to maintain the atmosphere of a home."

And that there is. Outside, the four-story, 14-bedroom house (now combined with the Blair Lee House next door) is cream-colored and black shuttered in an unostentatious Washington townhouse way. Only a few simple plaques on the wrought iron fence announce it as something beyond the ordinary.

Inside it is elegant, full of old books and antiques and lace curtains and a quiet charm. It is a home where tea should be served, and probably was on summer afternoons.

Edith Blair, in her white sandals and pink and baby-blue blazer and skirt, seems as much a part of the house as she really is, even though she says "Jeepers" a lot and admits it does seem "weird" having ancestors on the walls.

As she meanders through the old-fashioned rooms, she tells anecdotes about the furniture in Uncle Gist's study or chatters about the redecorated dark red library where Menachem Begin ate his breakfast.

Yes, it really seems like a home, even though Edith Blair must do big-hotel sort of things like ordering 50 pounds of flour and 40 dozen eggs before a typical visit that can cost the State Department from $4,000 to $6,000 for a three- to four-day stay.

The eggs and flour are just the beginning. Take a tentative visit by the Irish in November, for instance. Blair and her manager, Mary Schneck, will begin preparing days ahead of time, ordering the food and hiring extra staffers to add to the existing 11. From the house service to the rugs to lunch to hand soap, every detail is meticulously attended to. Fresh flowers and fruit must be placed in each room, the head of state's sheets - monogrammed with BH and trimmed in brown - must be clean, the bathrooms stocked with essentials, the desk with pens and paper. And of course the cards, delicate hand-lettered signs with each guest's name are to be slid into place on the bedroom doors.

The details are endless, down to the pink patchwork quilt on the chaise lounge in the queen's suite that must be clean and folded, or paintings like the childishly pastoral oil Dwight Eisenhower did that must be dusted and straightened.

Then there's security. The Secret Service and State Department swarm over the house in the days before a visit, setting up wires and communications equipment. Two hours before the visitors arrive, the house is "sealed" meaning everyone who belongs there must wear identification pins to prove it. "I practically wear mine on my pajamas," says Blair, who sleeps in the house during state visits.

During a stay, guests have 24 hour room service and are treated like royalty, which they often are. Afterward, they traditionally shake hands with the staffers and sign a black leather guest book. That reads like a Who's Who in global politics.

Says the guest book entry from Menachem Begin on March 5, 1979:

"In deep gratitude for the wonderful hospitality...we felt like we were at home."

Says Edith Blair, modestly: "Heads of state, heads of governments, are very easy to please." CAPTION: Picture 1, The Blair House drawing room in 1942; Picture 2, Edith Blair, inset, by John McDonnell - The Washington Post