More than instant history

History doubtless needs its instant reactors - the journalists with their very portable typewriters and cameras who wait for a scene to explode and then rush there to tell us all about it. Fast! And with much shouting, as if absolutely nothing else was happening anywhere else on planet earth except this . . . this headline.

When Lebanon was it, it was nothing but Lebanon. For a week the world became Grenada. Now the map of the globe finds El Salvador as large as China and the Soviet Union on the scale of journalistic obsessions.

Once upon a time South Africa was a hot spot too - one of the lead stories of the moment when black students were being killed outside of Johannesburg. And then, in September 1977, Steve Biko, the young leader of the black-consciousness movement's nonviolent fight against apartheid, was beaten to death in his cell, and journalists had their favorite kind of history - a charismatic figure (as they say) to go with an issue. But after a few lessons about apartheid, the nervous pointer finger of instant history moved on. There was in 1977 the Panama Canal Treaty to brood about. And how could anybody remember Steve Biko long in the year when Elvis Presley also died?

We recognize a terrible injustice in the jerky, discontinuous way journalism feeds us history when somebody gives us something more, as June Goodwin has done with South Africa in her new book, ''Cry Amandla!'' (Holmes & Meier, $22.50 cloth, $11.50 paperback).

In that summer of 1977 Miss Goodwin had just completed her first year in South Africa as correspondent for The Christian Science Monitor. ''Amandla'' is the word for power that crosses all African languages. Miss Goodwin had begun to hear it, like the everpresent hum of an electrical utility wire. But in her book she restricts herself to considering the power generated by, and against, apartheid among a cross section of South African women.

There are Afrikaner women speaking in these pages who equate apartheid with the Bible.

There are Afrikaner women who voice qualified doubts.

There is Helen Suzman, a member of South Africa's Parliament since 1953, five years after apartheid was established, who tells Miss Goodwin: ''If we had deliberately set out to produce a criminal society, we couldn't have done better than this country.''

There is an upwardly mobile black woman who speaks seven languages and owns a house, a car, and a color TV but, as a black woman, is treated as a permanent minor under South African law.

There is, above all, Thenjie Mtintso, a colleague of Steve Biko in the black-consciousness movement. Miss Goodwin interviewed her again and again, talking with her in jail and after she fled into exile. ''Her courage was awesome,'' Miss Goodwin writes, declaring flatly: ''She is the heroine of this book.''

Clearly Miss Goodwin is not objective. Has anybody been objective about apartheid on either side?

But South Africa changed her life, and she wants it, in a lesser way, to change ours. She thrusts its flowers under our noses, like the cosmos growing wild across the fields - ''the petals, wine-colored or white, with seams like valentine folds.'' She fills our ears with the continent's primal roar when Chief Buthelezi flicks his tribal stick amid thousands of stamping Zulus, swinging knobkerries and chanting during their annual gathering in a soccer stadium outside of Johannesburg.

She makes us feel the preciousness of this place, and the preciousness of its people, above and beyond the cruel waste of racial divisiveness.

This is journalism where the witness doesn't pack up and go away, and that act of constancy gives passing history a dignity, and even a sense of promise.