IOWA CITY, IOWA -- Writers, a fragile species, are insatiable for nurturing and coddling, and will go anywhere to find it. The finest anywhere may be here -- the International Writing Program, run by Paul Engle and Hualing Nieh Engle. For 20 fertile years -- more fertile even than the local corn- and bean-fields in this part of southeast Iowa -- nearly 700 poets, novelists, playwrights, critics and essayists from 71 countries have been served by the Engles.

The couple has raised $3 million in private and public money. Since 1967, it has been used for plane tickets and meal tickets or whatever else was needed for the proper vetting of innovative spirits and creative minds. For periods ranging from three to 10 months, the writers, and often their families, lived in a University of Iowa dorm that overlooks the Iowa River and an oak forest beyond. Some write, some think, all grow.

Last week, about 100 of the alumni returned for four days of merriment and gratitude to celebrate the program's 20th anniversary.

The high seriousness of speeches and panels was controlled by Paul Engle. Jaunty at 79 and still a boom-voiced, large-shouldered North Forty of a man, he has been a teacher of writing, a befriender of the forgotten and a prairie philosopher for more than 50 years at the university. At two evening dinners, Engle saw to it that plates were loaded and glasses filled. Then he gave the writers what they most hungered for, an open mike.

Katerina Anghelaki-Rooke, a Greek poet from Aegina, one of the Saronikos Islands, came forward to remember her stay in Iowa in 1974: ''The year I spent here was really the last year of my youth. I was 36. I dragged it out as long as I could. The Engles are my literary godmother and godfather. It was an intellectual holiday, it was paradise. The last day, I met a poet from Africa and we talked and understood each other naturally. No long explanations were needed on what we meant.''

Moshe Dor, an Israeli poet, journalist and author of 20 books, recalled that his year in 1970 was ''the first time ever that I could devote myself to writing. It was one of the happiest periods in my life.''

A Rumanian novelist, Nicolae Breban, was here last week. After returning home in 1978 he wrote to the Engles: ''For my friends in Iowa City . . . here are my enduring and warmest feelings. Also my affectionate thanks for the beautiful gift, which was the discovery of America, the America of farmers, of universities, of poets, America of great and (above all) of little cities, America of us fools, the last great sentimentalists. Friendship, friendship, forever.''

Other writers performed. A Japanese poet recited verse, a Nigerian novelist danced, a Korean poet sang. Fourteen members of the Mesquakie, an Iowa tribe and called ''people of the red earth,'' chanted, tom-tommed and danced. Engle joined the revelry. The first evening he recited scripture in a wry tone to remind everyone that writing has been the primal art since time began: ''In the beginning was the Word. Remember that. It wasn't 'In the beginning was a painting' or 'In the beginning was a symphony.' It was 'the Word.' ''

Engle, the son of German horse farmers and raised in nearby Cedar Rapids, tells funny stories that reveal an old farm boy sense of humus. Watching his father in the barnyard, he learned that shoeing horses is like writing poems: ''A work of art is first of all work.''

In ''The World Comes to Iowa: the Iowa International Anthology,'' a volume published this month, the Engles recall some of the writers they have hosted. Many have been jailed, censored or exiled. The program has taken in ''the world's horrors, fears, beauties, savagery, even triumphs, all at a level of intensity seldom known in the United States. The wounded come, scars invisible except in their eyes. For many, writing is not simply a career of words, but a matter of life or death. For some, the Iowa Writing Program is the first time they have not worked at some job to make a living, or had to worry if Big Brother was watching. One afternoon a writer came into our office and shouted, 'This is a great day.' 'Was your book published?' 'No,' he answered. 'This is the first time I walked here without looking back to see if I was followed.' ''

Few writers in America realize the breadth of their privileges. Thousands of newspapers and magazines, hundreds of book publishers and scores of agents are available. The Engles, both well published in fiction and poetry, traveled the world recruiting the ignored or censored. Come to Iowa, they said, it's on us.

What literary calling, whether producing novels that take years to finish or daily journalism that needs only hours, is higher than giving voice to the voiceless? From Iowa, the world has been listening to itself.