DELICATE hints of her Scottish origins still linger in Janet Brown's speech -- when she uses her own voice, that is. But this impressionist, comedienne, and actress is master of many voices, not to mention faces. One moment she may be intoning the stretched and gravelly vowels of Carol Channing, and the next, tearfully grasping at the catch-in-the-throat drawl of ``Dallas's'' Sue Ellen. Just as suddenly, she becomes stentorian in the persona of Barbara Woodhouse, English dog-trainer extraordinary: ``Si-TT! Sta-YY!'' Also in her repertoire are the voices and personas of Marlene Dietrich, Katharine Hepburn, Dolly Parton, and Queen Elizabeth II.
But it is unquestionably Ms. Brown's impersonation of Prime Minister Margaret Thatcher -- with that so indelible, so deliberately authoritative, so low-slow voice -- that tops the bill.
Her ``Maggie'' Thatcher has brought Brown a more widespread, peculiar kind of celebrity here in Britain than ever before in her career and a growing reputation abroad.
The fame has come -- as her just-published autobiography, ``Prime Mimicker'' (Robson Books, London), delightfully chronicles -- at the peak of a long, varied stage career that dates back to the '30s, when as a stage-struck 13-year-old she impersonated Shirley Temple and Mae West.
It was then that she won a talent contest in Glasgow and joined a touring show. Her concerned parents finally had to go and bring her home -- though by then the theatrical die had been cast. She was soon to be entertaining the troops during World War II and doing comedy work on radio, on stage, and in television.
The first time she did ``Mrs. T'' was when that redoubtable woman was elected party leader by her fellow Conservatives in 1975. This initial impersonation was anunscripted, last-minute performance for an early evening TV show. It was immediately noted by the press. With increasing sophistication and wit (and remarkably little unkindness) she has since developed it into a living cartoon strip of Britain's first female prime minister.
One of the hazards of Janet Brown's profession as an impressionist is that sometimes people get confused (or pretend to) about her real identity. ``I'd go to buy a rail ticket,'' she writes in her book, and the clerk would say: `` `Well, Maggie, where are you off to today? Aren't you supposed to be in Germany?' I'd hail a taxi, and, depending on the driver's politics, I would hear, `Jump in, Maggie,' or `I'm not giving you a lift.' It was all good-natured fun, and I enjoyed it.''
Her impressions of Mrs. Thatcher have led her into some strange waters. One time she addressed a congress of socialist (vigorously anti-Thatcher) trade unionists. They chanted, ``Get off! Get off!'' until they realized it was a sendup, she recalled. The laughter then became as vocal as the insults had been -- except for one ``stony-faced woman'' who came backstage afterward to say: ``I'm sorry, but I can't shake hands with you. You're too much like the real thing.''
On another occasion, which has achieved a certain fame in the United States, she played Thatcher in an extravagant hoax perpetrated on comedienne Joan Rivers in Los Angeles. Johnny Carson was at the back of this secretly taped spoof. But it was Brown's utterly convincing Thatcher and her gifts as an ad-libber that took in the razor-sharp Miss Rivers completely. Rivers, not famous for her politeness, was crushingly civil to ``Mrs. Thatcher.'' Once the joke was exposed, she unpredictably took it with great humor, allowing it to go out on American TV three times. ``If you dish it out,'' she said, ``you have to be prepared to take it.''
Politicians are not known for shunning publicity, favorable or otherwise, so it should not be surprising that since 1975, Thatcher 1 and Thatcher 2 have corresponded affably and arranged meetings on a number of occasions. Brown's book tells of several amusing encounters. The prime minister's TV image had suggested to Brown, before they came face to face, that she was ``a rather aloof, rather cold lady.'' So she was surprised to find that Thatcher was ``this woman with this great warmth,'' who struck her above all as ``motherly.''
One of Brown's favorite studies is the behavior of politicians. She enjoyed recently watching Thatcher's skill during a serious television interview. Usually very solemn and intent herself, this time she suddenly saw the funny side of the interviewer's strategy.
``He was very gentle but very persistent. He asked her a question at one point. . . . She's become so sharp! She said to him -- [and her own voice disappears immediately into the drawn-out Thatcher tone] -- ``You leaned in there, Mr. Dimbleby. Did you think you were going to ca-atch me ou-t?' The interviewer burst out laughing.''
Perhaps ``Mrs. T.'' learns something about quick repartee from Janet Brown. Who knows?