TAKING SIDES; The Education of a Militant Mind. By Michael Harrington Holt, Rinehart and Winston. 264 pp. $16.95; CUTTING EDGES; Making Sense of the Eighties. By Charles Krauthammer. Random House. 221 pp. $17.95.

IN TURGENEV's masterpiece, Fathers and Sons, Bazarov, the young medical student who represents the cynical and nihilistic "sons," relentlessly criticizes "our so- called progressives and reformers" who "never accomplished anything." Nikolai Petrovich, the cultivated, poetry-loving "father," claims that he has done everything to keep up with the times. "I have done well by the peasants, set up a model farm, so that all over the province I am known as a radical . . . and yet they are saying I'm over and done with."

Turgenev knew that the central conflict in the modern era is the conflict of generations. And that conflict is, as much as anything else, a conflict over habits of mind. It is still the tough- minded versus the tender-hearted. In the case at hand, Charles Krauthammer, who was trained in medicine, is the young, rigorously analytical "sense-maker." Michael Harrington, who started out as a poet, is the passionate, idealistic veteran of over 30 years of political activism.

Hold on a minute. It is Harrington who describes himself as a "militant" and a "radical." He has been a card-carrying socialist since 1952 and is a leading figure in the Socialist International. Krauthammer defines himself as a traditional (Henry) Jackson Democrat, a moderate, a lover of ambiguity who mourns the loss of the vital center in American politics. He resists radical solutions and, on almost every page of his book, attacks ideologues who insist on "taking sides."

Remember, however, we are not talking about political philosophies. We are talking abouthabits of mind. And from that standpoint, the contrast could not be sharper. Krauthammer, the "son," is the aggressive rationalist. Harrington, the "father," is the dreamy utopian. In Krauthammer's collection of previously published essays, we get the cold-blooded moderate; in Harrington's collection, we get the warm-hearted radical.

Krauthammer says he has an "allergy to fashion." Among the fashionable enthusiasms he skewers in his book are: comparable worth, Third World revolution, the nuclear freeze, nuclear and ecological apocalypticism, the "New Ideas" fad, the notion of moral equivalence, Nicaragua-chic, the theory that the United States lost the "moral high ground" when it intervened in Grenada, the idea that mental illness is a "myth," the Catholic bishops' pastoral letters on nuclear weapons and economics, one worldism and Jane Fonda's body worship. Occasionally he takes a swipe at a conservative target -- the right- to-life movement, right-wing isolationism and, with caution and an apology, football. But it is fair to say that he concentrates his fire on the fads and foolishness of the left, most of which deserves exactly what they get.

What they get is "Krauthammered." That is the intellectual equivalent of a multiple warhead -- relentless logic, devastating wit and sharp, clear, diamond-hard prose.

On abortion, for example: "When Geraldine Ferraro . . . says she's 'personally opposed' to abortion, she means this: I wouldn't have one myself and I wouldn't want my children to have one, but I won't go around telling the people whether to have one or not. Unfortunately, Ferraro is confusing belief with practice. If a person says, 'I refuse to own slaves, but I won't go around telling others what to do,' it is correct to say that he does not practice slavery, but can one really say he is opposed to it?"

On Jane Fonda, who reveals that she once suffered from an eating disorder: "It is too impolite to suggest that her current 'activist' incarnation is yet another internalization? Does this woman never stop eating? Having ingested the values first of Roger Vadim and now of Tom Hayden, she delivers with mind- numbing seriousness the startling message that one should never take one's values from others."

EVEN THOUGH Krauthammer claims that he is "not accepted in the (neoconservative) church," most of what he writes is animated by the spirit of neoconservatism. That doctrine of disillusioned liberalism has been kicking around for 20 years now. Why do we need to hear it all again? Krauthammer's achievement is to endow the neoconservative critique with fresh and original insights, and even some much needed subtlety. While the targets he chooses are, for the most part, predictable, his reasoning and perceptions are not.

Neoconservatives share the strange delusion that the left rules the world. That may be true if one's world consists of Cambridge or Berkeley or the New York literary intelligentsia. But as a way of "making sense of the eighties," I'm not so sure that perspective helps. Ronald Reagan is, after all, president and the conservatives have taken over Washington. Economics dominates the political agenda, and the Reagan Revolution is trying to transform the role of the federal government in American life. None of this gets much attention from Mr. Krauthammer. He is still obsessed, as most neoconservatives are, with the fallacies of the left. And it is on foreign policy, above all, that those fallacies are seen as most serious.

Thus, Krauthammer offers a bold defense of interventionism: "The West, of late, has taken to hiding behind parchment barriers as an excuse for inaction when oppressed democrats beg for help. The Reagan Doctrine . . . announces an end to inaction." In the most provocative essay in the book, he brands as isolationists those who claim to have learned something about the limits of U.S. military power from our tragic Vietnam experience. These include "right isolationists" like Secretary of Defense Casper Weinberger and the Joint Chiefs of Staff. They feel Vietnam recklessly endangered U.S. security by leading us to make military commitments where we had no compelling national interest. The response of "right isolationists" is nationalist and unilateralist: Take action only if our own national security is threatened. Don't be drawn into commitments just because they serve the interests of others. And don't fight unpopular wars.

Most "left isolationists" still support internationalist goals, only now they call them human rights rather than democracy. However, by renouncing the use of force, the left has given up any effective means of obtaining those goals; all they can do is punish our friends. Krauthammer holds fast to the unfashionable Cold War idea that "it is American power that guarantees the survival of freedom." The lesson he learns from Vietnam is prudence: "We will bear not any burden, but only some burdens -- those within our (relatively) reduced means -- for the success of freedom." The test he proposes is that, to win U.S. military support, a movement must be genuinely democratic and popular. The Contras in Nicaragua pass the test without difficulty.

Now one certainly shouldn't learn too much, or the wrong lessons, from Vietnam. But I think Vietnam raises issues that are much more serious than "prudence." It is impossible to ignore the moral dilemma that tore this country apart for 10 years: whether the ends justify the means. What kinds of measures would we be willing to take? As the doctors say, "First, do no harm." What kinds of people are we prepared to support? It would be nice if we could assure ourselves that only democratic and popular groups would get our support. I have a feeling, however, that many policymakers have a simpler test.

Krauthammer identifies with the tradition of liberal internationalism that once prevailed in the Democratic Party: "Liberal internationalism is a passion for democratic principles, and for bold interventionist Government to carry them out." He claims that "Vietnam destroyed that consensus." Neoconservatives think the Democratic Party is weak because it lost them on Vietnam. But I've got news for them. The Democrats took their advice on Vietnam, and that's what got the party in trouble.

The Democratic Party establishment -- Kennedy, Johnson, Humphrey -- also accepted the liberal internationalist line on civil rights and economic policy ("big government for big enterprises, at home and abroad," in Krauthammer's brave words). And look what happened. The Truman Doctrine led to Vietnam. Civil rights gave rise to a ferocious racial backlash that spread from South to North. The Great Society was destroyed in the 1970s by hyperinflation. Krauthammer asks, "Whatever became of the American center?" -- that is, liberal internationalism. He then proceeds to ignore much of the answer. He has nothing to say about race and little to say about inflation. And yet, I would argue, they had much more to do with the downfall of the Democratic Party than its rejection of interventionism.

MICHAEL HARRINGTON's career was also shaped by the trauma of the left. His is an unusual vantage point: he became a socialist during the 1950s and thus represents the intermediate generation between the radical ascendencies of the 1930s and the 1960s. McCarthyism was his formative experience. In his 1955 essay attacking the American Committee for Cultural Freedom (ACCF), he accuses the liberals of selling out to McCarthy and doing little to defend either civil liberties or cultural freedom. He was at that time, he says, "hostile to both Stalin and Joe McCarthy."

The 1960s were another period of deep personal anguish for Harrington, when once again he "took sides" against the prevailing tendencies of the left. He called it "a disaster" that the peace movement had stopped taking the issues of ati-communism seriously. "It is the most dangerous unradical isolationism," he wrote in 1965, "to say that a peace movement -- whose concerns must be global -- has no obligation to think about this enormous concentration of political, economic and military power is for good or for bad." He also critic w0'ngton relies on an impending economic catastrophe as the only hope for reviving a left majority. Krauthammer sees no future at all for traditional liberalism: "It will likely fracture along existing political fault lines and disappear into the landscape." Neither of these options is encouraging. Meanwhile, Harrington is "deeply involved in the nuclear freeze movement and in the struggle against American intervention in Central America," while Krauthammer is on the other side of both issues.

Thus, two men who share so many values and sympathies remain far apart, separated by a vast generational space that defines their habits of mind. That is the tragedy of the American left. It is also the tragedy of fathers and sons.