Moving through the snowbound, windblown steppes of Washington yesterday. Nicola Pagett - alias "Anna Karenina" - was expressly civilized, polite, beautiful and sane. She goes out of her way, Pagett says, to live a relentlessly ordinary existence when she is not traipsing around as some period Tragedy Queen such as Anna - Tolstoy's aristocrat who falls in love, has a nervous breakdown, gets addicted to morphine, drives her lover from her when she becomes "positively ill with jealousy," then flings herself under an onrushing train.

Pagett's only problem is filming the classic for "Masterpiece Theater" was revving up emotionally for scenes shot out of sequence. "I had to die - before I met the man I died for." Becoming "pregnant" by her lover was no problem. "Although everyone on the set knew it was a pillow," in her advanced stages of pillow-hood, "everyone kept offergin mt chairs, averting their eyes."

Pagett is the latest of Britain's Masterpiece Theater stars who have become American celebrities. Pagett, like many of the others before her, is somewhat astounded at the reception here - from The "Today" show to autograph-seekers rushing up to her in airports to impromptu ovations in a New York restaurant over the weekend.

"In England there is not this movie star lifestyle. So you have to do the grocery shopping and all. I like incredibly ordinary things. It is absolutely necessary to keep in touch with day-to-day reality when you act for a living. It's very difficult not to be self-obsessed when what you're doing is selling yourself. My idea of relaxing? Sitting down after having cleaned the whole house."

Such talk from Anna Karenian.The saving grace is that Pagett does speak in those italics has looks way beyond the ordinary and an acting ability to match.

She shrugs off a description in Time magazine: "Her eyes have a slight goldfish bulge, her lips are too full, and her cheekbones are uncommonly high. Pagett says, "I didn't mind that - it's quite true." But it all adds up to, as the magazine also stated, a "strange beauty." Her face looks sensuous one moment, pixie-ish the next.

Only 5 feet 2, Pagett dresses simply in a baggy tan turtleneck and skirt and boots. The most dramatic thing about her is her long green cigarette holder. Her manicured nails are not lacquered, she wears but one ring, a thin wedding band. Pagett, 32, has been married for eight months to a former actor. Graham Swannell, now a "struggling playwright" who quit acting because "he didn't like all the razzmatazz." There is no professional jealousy, says Pagett, in that by now famailiar recitation of her ordinary life. "I am married to the most supportive person."

Pagett was last seen by American audiences in the early episodes of "Upstairs, Downstairs" as the Bellamy's strong-willed daughter who moves to America - and out of the series. She was written out early at her insistence. She feared type-casting and did not want to be shackled that long to one series. "Nothing more could have happened to me anyway. I could see the writers saying, 'What the hell do we with her now?' There I would have been, ringing up Hudson on the intercom forever."

Pagett cannot remember a time when she didn't want to act. Standing on stage in her first part, Snow White, at age 8, she says, "I felt as if I belonged there."

She was playing Snow White in Yokohama at a convent school before an audience of "nuns, mums, and dads." The daughter of a "moving around" Shell Oil executive, Pagget was born in Egypt, lived in Hong Kong and Yokohama before returning to English boarding schools at age 12.

"My mother then wanted me to go to finishing school. I didn't. What would I be going for . . . to speak fluent French and ski!" Instead she auditioned for the Royal Academy of Dramatic Arts (RADA) at 17, studied there for two years and moved almost effortlessly into West End repertory, TV, and movies She stared on stage with Sir Alec Guinness three times, and has acted both Shakespeare and modern comedy.

Her secret wish is to play more comic roles. She likes wry humor that is an exaggeration of life rather than off-the-wall comedy such as "Monty Python." I call that "anxiety humor, neurotic humor I don't think that's funny at all. I saw Carol Burnett the other night. Now that's the kind of humor I like."

At WETA (Channel 26) Pagett patiently taped a two-minute spiel to drum up funds for the station's pledge week - changing the copy to downplay herself.

She finds publicity tours hard. "I don't like the superficiality of meeting people - and then just going on." England is less tolerant of success and more sympathetic to failure than America she feels. "Here, if you're any success the world opens up - but if anything goes wrong, watch out. Some English actor friends tell me about being here once. The actors in the good play went to all sorts of parties. Those in the bad play didn't get asked anywhere."

Pagett studied Tolstoy's Karenina and decided that she should not be played for sympathy.

"The point is, she could have gone on and had her affair on the quiet and nobody would have minded. But she wouldn't do that. She was not spineless. She was completely rounded. She has her faults but at least she was real."

Pagett does not know what her next part will be, but she is hardly worried.

"When you're cast well," she says with an extra ordinary smile of self-confidence, "it always becomes a wonderful part."