EASTSIDER JEAN MARSH Creator and star of _Upstairs, Downstairs_ 2-10-79 _Upstairs, Downstairs_, the saga of a wealthy London family and its staff of servants in the early years of the 20th century, is one of the most popular television series ever filmed. The first episode of the British-made series was released in England in 1971, and since that time more than one billion people in 40 countries have watched the exploits of the Bellamy family. Introduced to American public television in 1974, _Upstairs, Downstairs_ won seven Emmy Awards, including one for Best Series each year it was shown. If any single performer could be said to stand out over all the others, that would be Jean marsh, who received an Emmy for Best Actress for her portrayal of Rose, the head parlormaid. But what most of Marsh's American fans fail to realize is that, with her, without would be no _Upstairs, Downstairs_: she co-created the show with another British actress. A New Yorker on and off for the past two decades, Jean Marsh now lives in an apartment on Manhattan's Upper East Side. It is here that I meet her to talk about _Upstairs, Downstairs_, which returned to American television in January with 39 hour-long segments, eight of which have never been seen before on this side of the Atlantic. "Sometimes it drives me crazy that nobody ever speaks to me about anything else," says Jean, a slender, pretty, soft-spoken woman who has the knack of putting visitors immediately at their ease with her charm and lack of pretension. "I start to drivel after a while, because I tell how I devised _Upstairs, Downstairs_ and how the cast was chosen." There is no irritation in her voice, only humor. With her lively eyes and childlike appearance, she is reminiscent of Peter Pan. _Upstairs, Downstairs_, says Jean, "didn't spring new-minted. My friend Eileen Atkins and I had been talking about trying to devise a television series. We thought we should write something we knew about -- about our pasts. And it became servants more than anything else, because her father had been a butler. She was showing me pictures of her family one day; she had photographs of servants going to a pub in a horse-drawn bus. So the first thing we wrote about was servants going on an outing. And later we decided it wouldn't be nearly as interesting unless we included the people upstairs."