WITH A SNAP, Colman McCarthy lays his journalistic cards on the table. "I am a

pacifist, a vegetarian, a Catholic trying to become a Christian, a bicyclist and a runner," he writes in the preface to this latest collection of his articles and columns. Elsewhere in its pages, the reader learns that McCathy has put in time as a Trappist monk (he now has a wife and three sons), a speechwriter for Sargent Shriver, and a street person. Oh, and that on Halloween he gives out vegetables -- potatoes, carrots, onions, and, one nightmarish year, okra.

McCarthy writes a syndicated column, with The Washington Post as his home base, but as the new sampling of his facets indicates, he is not a traditional pundit. He continues to file stories as a reporter but doesn't buttonhole senators or cabinet members in search of material (though he once gave a general the finger when his helicopter buzzed the monasterial pasture where Monk McCarthy was tending cows). His heroes tend to be rebels like Daniel Berrigan or quiet movers like writing teacher Paul Engle and the late Dorothy Day and rather than stars or politicians. As the book's title suggests, McCarthy enters into his journalism -- so much so that on occasion editors have killed his stories to obviate conflicts of interest.

Whereas most columnists tend to be either personal (Russell Baker, Erma Bombeck) or analytical (Joseph Kraft, David Broder), McCarthy is both. He could write about the homeless before practically anyone else because he encountered them regularly in his one-morning-a-week volunteer stint at a local soup kitchen.

When he discusses the trickle-down theory of economic distribution once propounded by the Reagan administration, his arguments rest on firsthand experience. In 1982 he went to Chicago, left all the "trappings of middle-class life in a locker at the Greyhound terminal," and hit the streets as if they were home. The outcome was a fine, long piece of reporting (it first appeared in the The Nation) that provides shuddering insights into the hell of destitution.

One night McCarthy found shelter in a mission where the quid pro quo was hour after hour of religious indoctrination. At bedtime a guard, referring to him by his cot number of 7-A, reminded McCarthy to check his clothes in the hot box, a room where the heat is turned up to kill lice and other vermin. All night long his fellow waifs wheezed, coughed, moaned, muttered, shouted. T

HE NEXT NIGHT he spent in

jail after two benevolent cops

agreed to make a bogus arrest.

All of his possessions were confiscated, including the volume of poetry he was planning to read. Luckily, he got a bunk. But "voluntary arrests" were thrown in with petty criminals, who "for hours . . . screamed at one another, asserting their manhood. Sometimes a man would roar his hatred for another prisoner, ten cells away. On the rare occasions when the guards intervened, they added their shouts of 'Be quiet!' to the general uproar. Through the long night the voices -- raging, threatening -- never stopped. Once again, the poor were venting their anger at the only available target -- one another."

In another piece he quotes a nun on the limitations inherent in even the most humane shelters. "There are some (people) out there . . . who might be called sub- hopeless. They won't ever come to a shelter or if they do come they are violent and we have to ask them to leave. We're not really getting the worst of the worst."

It's a bit jarring to pass from sobering dispatches like these to McCarthy's feuilletons on running. In his defense, however, let it be said that running is a small- is-beautiful sport and thus consistent with his antipathy to the lavish and bloated -- and that he was doing it when Yuppies were still a gleam in Madison Avenue's eye. The running section, incidentally, is the only place in the book where McCarthy admits to abandoning cherished beliefs. Confronted with the damage all those aerobic miles can wreak on knees and joints, he now wishes he'd confined himself to a couple of marathons a year instead of the four or five to which he used to sentence himself.

Given his mindset, it would behoove McCarthy to exert iron-willed control over his jerkable knee. This he does not always do. At his worst the predictability of his views begets treacly prose. He spoils a good piece on Eddie Stanky, a once pugnacious baseball manager who later decided it doesn't matter where nice guys finish, with a stock, sentimental conclusion: "He believes that games are not only a way of enjoying youth but of getting beyond it as well, so that when the other delights come along -- education, raising children, tears at graduation -- we will be wise enough to value them."

Happily, lapses like this one are rare -- and overshadowed by McCarthy's eagerness to upset nearly all the establishment's unexamined tenets. I can't help noting, however, a glaring inconsistency between his pacifist philosophy and his personal behavior. Where I come from, handing out okra to trick-or-treaters would be a declaration of neighborhood war.