ROBERT MacNEIL is one of a half-dozen television broadcasters in the United States who insist on speaking English as they learned it at their mother's knee. In Mr. MacNeil's case it was in Halifax, Nova Scotia, which explains the quaintly un-American touch he often brings to ``The MacNeil/Lehrer NewsHour'' on public television.
``I was enormously lucky,'' he said during a recent visit here, ``because my mother was enthusiastic, and read with great fervor and delight. And I think a lot of the books ... like Dickens ... she was reading for the first time herself, so it was very exciting.''
Robin (as his friends call him) MacNeil and his wife raised four children - and managed to preserve Robin's family tradition of reading aloud.
``It was a little harder,'' explained MacNeil, ``as we got into the television age with our youngest son, who, when invited to hear my rendition of my favorite, `Treasure Island,' responded brusquely, `Naw ... I saw that on television.'''
The lad was not won over until father and son shared a boat trip and MacNeil set aside an hour every evening to read ``Treasure Island'' aloud.
``Parents can plant magic in a child's mind,'' he said, ``through certain words spoken with some thrilling quality of voice, some uplift of the heart and spirit.
``It's very hard to compete with television these days,'' he added with feeling, ``but I think if you persevere and make daily reading the occasion of your intimacy with the child, and something predictable and routine, you can still do it.''
``If you love the language,'' MacNeil writes in the just-published second volume of his memoirs, ``Wordstruck'' (Viking Penguin, New York, $18.95), ``the greatest thing you can do to ensure its survival is not to complain about bad usage but to pass your enthusiasm to a child.'' BUT what if one finds little to be enthusiastic about in the imprecise verbal shorthand that passes for speech today?
``If you confine yourself to the classics,'' he explained, ``you need never have doubts about what to pass on. I find it hard to imagine a child in any English-speaking country - no matter how besotted with television - not responding to the best of Kipling, Stevenson, Barrie, and Defoe.
``Their stories have endured because they're strong and dramatic, and they're deeply intriguing to children.''
Robert MacNeil's formative years in broadcasting were in radio in Canada, and although he readily concedes that radio in North America has been bypassed by TV, he insists that radio is peculiarly and wonderfully appropriate for some tasks.
``If you want good reading, conversation, analytical thought, poetry, or criticism, radio is perfectly the medium for it.''
But, perhaps surprisingly, he does not despair over TV's influence. ``Through television,'' he points out, ``more Americans hear more correct, even beautiful English ... than ever before.''
And Robert MacNeil and his ``NewsHour'' team continue to set a very high standard despite their good-natured wrangling over language.
``I was born and educated in Canada,'' he noted, ``but have divided my working life between England and the United States. So now I'm hopelessly confused in my spelling, vocabulary, idiom, and pronunciation.
``My American colleagues bring me up short all the time because I'm constantly using expressions I picked up in England and happen to like, such as `set the cat among the pigeons.'
``The other night I heard my colleague Jim Lehrer saying `AY-zores,' which is almost the standard American pronunciation for the islands in the Atlantic. But I couldn't get myself to say it that way because it's not my pronunciation. I stress the second syllable.
``But that's what language is all about. Almost every generation resists change although it's inescapable.''