The first few mornings I went running along the country lanes of this tiny slip of land off the coast of southwest County Kerry. I noticed farmers and countrymen scowling at me. Some looked away in disgust. One farmer, resting on his pitchfork in a hayfield, called out what I thought was an oath, as they say in the old Church.

I didn't understand these negative reactions. In America I was used to insults during my runs. This was supposed to be the land of merry leprechauns. I was used to insults, but only from beery louts in oversized cars. Then I realized the specticale I had created: the local Irish thought my white running shorts were my underwear.

That, indeed, would be typical behavior for the Ugly American: gadding about the turf fields and exquisitely beautiful seacoast half naked, and then covered up only with underwear.

Happily, my wife - whom I have on retainer as my wardrobe manager, now that I've done Boston - brought along a second pair of shorts, green ones. The morning I wore those. I heard nothing but cheers from the locals. I was blessed by a priest, greeted by a herdsman, smiled at by a group of colleens and asked in for lunch by the illustrious Sean O'Shea, a Kerry historian who knew Brendan Behan, Paddy Kavanagh and a wild line of Irish eccentrics.

For the rest of my time in Ireland, I kept to my green shorts. It is the color of St. Brendan, whose ancient hermitage looks out over the Atlantic and stares down the centuries from the eastern tip of Valentia.

I had come to Ireland for a few weeks of summer running. It is ideal for training for the autumn season of marathons. Temperatures never exceed 75. The purity of the air - the winds of cool sea spray blowing in from the cliffs of Dingle Bay with the Gulf Stream a few miles into the ocean - means that the lungs are refreshed after a run, not fatigued.

Hill work meant little more than climbing up the inclines of the island: Nearby on the mainland are the long rises of Macgillicuddy's Reeks, Ireland's modest mountain range between Killarney and Cahirciveen. For running into the wind, nowhere is finer than this part of Kerry, with its stiff breezes that bluster in after days of roughing up in the Atlantic.

On some days on Valentia - a name not from the Spanish, but the Gaelic Bheil Inse, the island beside the mouth of the river - the weather changes so quickly that for the first seven miles of a run from one end of the island I would have a sweatdrenched shirt. But then, coming back seven miles to the other end, the wind dried out the shirt.In a two-hour run, it is possible to have as many as seven or eight kinds of conditions: sun, rain, mist, wind, hill, flatlands, cowpaths and pastures.

I met only one other runner on Valentia. He was a farmer's son, a husky lad of think thighs who explained that he did his daily four miles only when in training for football. That sport - a more rugged style of play than American football, because the players don't rest for huddles, wear padding or otherwise avoid reality - combines with hurling as the nation's athletic passion.

Irish runners are mostly short-distance. Eamon Coughlan, a miler, won several races in America the past few years, including the CYO event in January 1977. The current world cross-country champion is John Treacy of Dublin. As for long-distance men, Ireland did the important work of providing the gene pool for the Kelleys, older and younger, of Boston fame.

If rural Ireland is a runner's paradise with few runners, Dublin is in sharp contrast. Phoenix Park, the pastoral haven-of greenness just beyond the main city, is as crowded as the Washington mall at noontime. The current American ambassador to Ireland, William Shannon, has a residence in Phoenix Park, and he has become a runner. He is keeping his head about it - doing no more than a couple of miles a day. In his career in Washington, in The New York Times bureau. Bill Shannon was mostly a sitter. Now he is a mobile diplomat, so that breed is improved.

While in Dublin for a few days, I took daily runs along the poiers in the suburb of Dun Laohaire. I mixed in with the crowd of other runners easily enough, but one afternoon I heard a voice calling out my name.I knew it wasn't someone mistaking me for Bill Rodgers, because my hair is darker. Instead, it was John Rowan, a Washington friend who lives three doors from me. He and his wife, Phyliss, were visiting Dublin. We had a few moments of pleasant conversation, but I have wondered how shocked they must have felt to see me, after the countless times they have seen me run by their house. "Even over here," they must surely have thought as I pounded along the pavement toward them, "we can't escape this nut. Are we seeing things? Is he following us around the world? Quick, there's a tree. Let's hide behind it. Too late. Well. Call out to him and we'll make the best of it."

Maybe they didn't think that at all. The Rowans Irish-born, are kindly toward all living creatures, including runners. Instead, they were much like all the Irish I met along the roads - lively, witty and happy to have a diversion from the day's routine. They were delighted, too, approving of my wearing of the green.