Isaiah Berlin -- a thinker we should know;

Perhaps the most remarkable thing about an interview with the philosopher and historian of ideas Isaiah Berlin is that it should occur at all. Certainly Sir Isaiah's conversation is as fascinating as one was led to expect; certainly he is as kind and polite as everyone said he would be.

But having an interview with this Oxford professor and thinker is rather like being a naturalist who comes across a rare species of animal after a lifetime's search: One must get over one's amazement at being face to face with him before one can begin to appreciate his particulars.

For like the rare animal that has eluded naturalists, Isaiah Berlin has been particularly and consistently successful at keeping journalists off his trail.

''I have granted very few interviews in my life,'' he explains in the living room of his London flat in an elegant building near Piccadilly Circus. ''I absolutely hate doing it. I loathe it. I always think they've got things wrong even if they haven't, and I want to take things back. I hate seeing my name in print in a newspaper or anything whether for good or ill. I'd much rather never be mentioned in any connection.''

So apparently acute is his feeling that one feels inclined to call off the whole project, despite the difficulty in arranging it, and leave him in peace. And yet once he has settled into a discussion of ideas, his aversion to the press seems forgotten.

After all, his wariness of the press has not prevented him from publishing the essays and giving the lectures that have made him such a desirable prey. His essay collections - including ''Russian Thinkers'' and ''Personal Impressions,'' his essays on famous people of the 20th century, most of whom he has known - were republished in recent years in the United States and Britain.

Isaiah Berlin has gained his eminence through the rare academic discipline of the history of ideas. A sort of philosophical ''geologist,'' he traces the patterns of thought in Western philosophy, digs down to discover the influences that helped mold them, and holds the ideas up to the light of his laser-like intellect to pierce them through as a test of their mettle. Berlin has interpreted philosophers; he has compared them; he has broken down ideas into their component parts and often found them to be less impressive than their surface glitter might indicate. He has written, for example, on the age of Enlightenment (Locke, Berkeley, and Hume), Karl Marx, Machiavelli, even the composer Verdi, and many others.

But, as he has done this, his own ideas on many of the great philosophical questions, such as freedom of the will and liberty, have emerged. Often he has chosen merely to emphasize or bring into the open the ideas of a thinker who has not been given his due.

Above all things, Berlin is against oppression (whether by governments or constricting ideas), and against accepting less than the truth, however elusive that might be. He is a celebrator of life, a disliker of abstractions - certainly not an ''ivory tower'' philosopher. If one were to have to formulate Berlin's attitude in three words, those words might be ''No easy answers.''

Isaiah Berlin was born the son of a Jewish timber merchant in the Baltic port of Riga in 1909. At the age of seven, Berlin watched the first stirrings of the Russian Revolution take place from the balcony of his parents' apartment in Petrograd. His family emigrated to Britain in 1919. They settled in the suburb of Surbiton, south of London, and Berlin has admitted the move was quite a cultural shock, even though he knew English when he arrived.

Eight years after his arrival in Britain, he gained entry to Oxford, where it became clear that his abilities were to place him in the intellectual stratosphere: Though he didn't quite know it then, Oxford would become the center of his life.

By the time of World War II the British government had decided to make use of Berlin's abilities by appointing him first secretary at the British Embassy in Washington. The wit, learning, and perspicacity of Berlin's dispatches made them among Churchill's favorite reading matter. Churchill wanted to meet the clever young diplomat, and thus ensued what has become the most popular anecdote about Berlin's life.

Because some hapless civil servant confused their names, Irvingm Berlin (the American composer) was invited to dinner at No. 10 Downing Street instead of Isaiah Berlin. The mistake was only noticed because Churchill later observed how little the wrong Berlin seemed to know about government policy.

After the war, Isaiah Berlin spent a brief sojourn at the British Embassy in Moscow and then held a lectureship at Harvard. He then returned to Oxford, where he has since served in many capacities, including president of Wolfson College from 1967 to '75. He married, at 45, a French woman. His main interests outside the history of ideas are music and the arts, and he serves on several boards in support of these activities.

Like any good professor, Berlin is firm but not patronizing with those less learned than himself. There are several false starts at trying to settle on a topic of conversation. But once Berlin does start talking, the words whizz by at a dizzying rate; one is swept through a forest of ideas.

Berlin agrees to talk about one of the things that has made him famous: hedgehogs and foxes.

This apparently unlikely topic was the subject of an essay he published in 1951, uninvitingly titled ''Lev Tolstoy's Historical Scepticism.'' It did not immediately take the world by storm, nor was it intended to. But it was the kind of rare essay that actually broke new intellectual ground, and it became of interest to a wider public than Tolstoy scholars. Indeed, it marked a place where the wide and nebulous territory of world thought became a bit more clearly mapped.

The essay was expanded and republished in 1953 as ''The Hedgehog and the Fox.'' The new title was derived from a quotation from the Greek poet Archilochus, on which the essay - which has nothing to do with zoology - is based: ''The fox knows many things, but the hedgehog knows one big thing.''

In the course of the now famous essay, Berlin attempted to show that Western thinkers and writers can be divided into two categories: those who were hedgehogs and in Archilochus's terms emphasized one central vision and the unity of the world; and those who were foxes and emphasized diversity, separateness, and uniqueness.

For example, Dante, Plato, Pascal, and Dostoyevsky are hedgehogs, according to Berlin's analysis; Aristotle, Goethe, Balzac, and James Joyce are foxes. The center of the essay is the argument that Tolstoy, a particular interest of Berlin's, believed he was a hedgehog but was actually a fox.

Seated in an armchair next to a coffee table neatly piled with academic journals, Berlin says he now has new thoughts about this essay 30 years after it was written: ''People have taken this dichotomy a little bit too seriously,'' he says with slight exasperation. ''There are people who are both hedgehogs and foxes, and there are people who are neither.'' But the fact that the categories are in no way absolute does not diminish their usefulness, he still believes.

''Foxes have a tendency to look at things mainly for [the things] themselves and are interested in a great many things because they are what they are. They're simply fascinated by the variety of the world and not its unity.

''Hedgehogs, on the other hand, are dominated by a single, coherent conception of the world, by some central idea to which they try to reduce everything,'' he explains.

''Everyone assumes in this essay that I sided with the foxes. I tried not to. I think I'm probably more of a fox than a hedgehog, but I don't want in many waym to deny the value of the great hedgehogs of the world - like Plato, who was an arch hedgehog - without him there might have been no philosophy.''

''The Hedgehog and the Fox'' essay is perhaps the best with which to begin to appreciate the nature of Isaiah Berlin's thought. Behind much of what Berlin believes philo-sophically is a concern with how ideas are applied to life; how, particularly, they influence politicians and ordinary men. Unlike those caught up in the trend for determinism, Berlin believes that ideas and individuals are crucial to history and that historical trends are not unstoppable tides. Another of his essays, ''Historical Inevitability,'' deals with this topic.

''I think individuals count like anything,'' he says. ''General trends and tendencies exist, and of course it would be foolish to ignore them. But one sees that there are certain turning points in history where the existence of certain people - for good or ill - has made a difference. I'm against those who think what happens must happen.''The world may never know what it has been like to be Isaiah Berlin. Although he is known to be outgoing and uninhibited with friends, there are no signs that he plans to reveal his life in an autobiography.

Berlin is a complex man and one not particularly optimistic about the course the world is taking. He believes in using the strict disciplines of philosophical inquiry to try to sift what is false from what is true, what is bad from what is good. But he does not believe in devaluing or undervaluing other viewpoints and other methods of inquiry. His is the compassionate, wide, and tolerant vision of a rather shy fox who takes kindly to hedgehogs.