Muggeridge: out of the cocoon; Like it Was: The Diaries of Malcolm Muggeridge, selected and edited by John Bright-Holmes. New York: William Morrow & Co. 560 pp. $18.

I'm glad I didn't fling Malcolm Muggeridge's diaries across the room, though there were moments, particularly at the beginning of the book, when I was sorely tempted. After all, even to decide to record all one's thoughts and doings demands a degree of egotism; as for the actual process, it can be destructive indeed, feeding self-pity. Certainly Mr. Muggeridge found it so. He spoke often of a desire to die. And people, he said when he was in his 30s, ''think I'm conceited and opinionated, whereas I'm only unhappy.'' He was right. They did.

But what makes these diaries fascinating to the determined reader is the chance to watch the writer escape from his dreadful cocoon. Since the diaries have been cut down to a mere quarter of their original selves, it is hard to tell whether the escape began as abruptly as an entry in August 1936 would suggest:

''I know that love governs the universe. Then what can there be to fear? I know that whatever success or ecstasy might be it would be dust and ashes unless I felt myself at one with God. Thus I shall seek this success, and if I fail to find it my life will have been failure, and if I find it, my life will satisfy. No other measure is applicable. It does not even matter to me whether I manage to express this sense of oneness. Yet, too, it is its nature to crave expression , and if I get it I shall express it.''

Depression is never completely routed, but from then on scattered through these pages are entries as joyous as his favorite hymn, ''Let us with a gladsome mind/Praise the Lord for He is kind.''

The diaries begin in the '30s, when Mr. Muggeridge went to Moscow to write free-lance copy for the Manchester Guardian, a disillusioning experience for a young man who expected to find the ''New Civilization'' in the Soviet Union.

Instead he found the system evil. ''Evil,'' he wrote, ''is the only apt word. Evil because there is no virtue in it; and because it has utterly failed.''

The year 1934 finds him in Calcutta, working for the Statesman, and observing that ''Soviet society is based on the lust of class hatred'' and that in India he could sense ''the race hate constantly'' being directed at him and his fellow Britons.

But though the events of his career -- his intelligence work in World War II, his editorship of Punch, his growing fame as a lecturer and broadcaster -- are sketched in here, they are told far more vividly in the first two volumes of his as yet unfinished autobiography, ''Chronicles of a Wasted Time'' (Morrow Quill paperbacks, $6.95 each). What makes the diaries fascinating to me is what they show of the development of the man himself.

I found bonuses, too. Mr. Muggeridge is a valuable source of revealing anecdotes and memorable quotations.

Here's Sir Winston Churchill, for instance, hearing that the ambitious Lord Reith wanted to see him and remarking: ''That Wuthering Height!''

Thomas Hobbes (the 16th-century philosopher) had a wonderful description of laughter: He saw it as ''sudden glory.''

Writer Hugh Kingsmill commented that ''Whenever you see 'No Exit' it means there is an exit.''

Research for his biography of Martin Luther convinced Brian Lunn that ''Christianity was the first religion to interest people in motives.''

''Time,'' said Maj. Gen. Sir Edward Spears, talking about Soviet puppet regimes, ''cannot preserve what time has not fashioned.''

Mr. Muggeridge's own wise words deserve quotation too:

''Everything is moods -- love, hate, convictions -- when you have no belief.''

''(One) characteristic of the power addict, I think, is to have no taste, since taste belongs to the individual soul and exists by reason of its separation from, rather than its identification with, the herd.''

He finds the Manhattan skyline ''the only architectural achievement of our time.'' He marveled at it, ''misty in the autumn light, exquisite in its unique, original way.'' But he adds a bitter note, sadly typical of the despair that overshadows so much of his diary. They are shaped, he feels, ''in the image of their own ultimate destruction. They convey the idea of time, not eternity.''

But listen to him in a more positive mood:

On the pleasures of abstemiousness, he writes, ''One should not give up things because they are pleasant (which is Puritanism) but because, by giving them up, other things are pleasanter.''

'' 'Life is too marvellous,' I say in one of my lectures, 'to be taken seriously, and truth too stupendous and luminous to be solemnly propounded,' and mean it too.''