Idylls and hardships of country life; Second Cutting: Letters from the Country, by Richard M. Ketchum. New York: The Viking Press. 192 pp. $13.95.

Well, if I had to chose one or the other, I'd choose to be a plain New Hampshire farmer With an income in cash of say a thousand (From say a publisher in New York City). - Robert Frost, ''New Hampshire''

Literary men since Virgil have extolled the virtues of farming and country life, and the more economically unfeasible the farm the more romantic the prospect seems to be. Robert Frost said that he taught at a college only so he could afford to farm in New England. So Richard Ketchum is in good company with this delightful volume of short essays reprinted from his monthly column in Blair & Ketchum's Country Journal.

For the most part he knows what he is writing about from hard experience. If he knows the joys of calving time, he is quite aware of gnawing cold, premature births, and the struggle to save newborn animals from the weather.

His delight in the January crop of seed catalogs is tempered with the despair of a man who can cast a cold eye on last year's squash. Thank goodness he doesn't idealize wood-burning stoves!

Mr. Ketchum is also aware that most New England farmers have less time to contemplate country joys than a man who can supplement his farmer's gain with an editor's income. He reminds us of the enormous capital investment farmers must make to be competitive and of the wretched return for their 16-hours-a-day, seven-day workweeks.

These essays are concerned with the broad spectrum of rural joys and problems. Mr. Ketchum is appalled that our farmland, the very basis of our culture, is being treated as just another quick-buck investment by developers and real-estate sharks. Indeed, it is this quick-money mentality that distresses him most. Whether the greedy machinations threatening small-town life are cooked up by big business, big government, or just big ignorance, he takes the culprit on with a prose style that rarely loses its sense of humor.

The humorous pieces reprinted here are a little better than Erma Bombeck at her best, with the long-suffering author always the unwitting victim. The more reflective essays raise many concerns familiar to readers of Wendell Berry. This is not to say that Mr. Ketchum is trying to capture the tone of either, but only to suggest the range of the book. His own prose style is neighborly, terse, usually cheerful with just enough crankiness for salt.

As much as we enjoyed ''Second Cutting,'' the book turns our thoughts to that annual migration of well-meaning folks who move to northern New England with lots of money from somewhere else. Having read too much about the idyll of country life, they pay a lot more for our old farms than our local farmers can borrow. Those who stay are among our countryside's best defenders, but too many move on in a year or so. Having learned that a farm is not a toy, they sell or subdivide the old homestead at a profit and move on to life's next adventure. It makes us wish that Mr. Ketchum had made country living sound even less idyllic than he has.