The thrust of Peter Beinart’s powerful and well-argued message in “The Good Fight” (HarperCollins, 288 pages, $25.95) is straightforward: The liberal left in America has abandoned its own best heritage for what Arthur Schlesinger Jr. once called “doughface liberalism.” These liberals oppose terror and totalitarianism but recoil against taking any necessary steps to defeat it, fearful that their moral purity might be stained in the process.

Mr. Beinart first took up his case in a lengthy article in the New Republic, where he was editor from November 1999 until March 2006. He has now sought to explore how and why a once vital and dynamic American liberalism – devoted to asserting American power on behalf of democracy abroad as well as at home – went soft and, in Mr. Beinart’s words,”preferred inaction to the tragic reality that America must shed its moral innocence to act meaningfully in the world.” He asks nothing less than that liberals (and Democrats) hark back to the much besmirched Cold War liberalism of President Truman, George Kennan, Hubert Humphrey, and others – and move away from the anti-interventionism of Michael Moore, George McGovern, and Howard Dean. The philosophical hero of “The Good Fight” is Reinhold Niebuhr, a man who gave up on pacifism. Niebuhr posited that Americans have to recognize their own capacity for inflicting evil by building restraints on un mitigated power, but not hesitate to act to prevent greater evils.

Niebuhr wrote about the crisis of the 1940s and 1950s, and Mr. Beinart asserts that Niebuhr’s careful balancing act still holds. Many liberals today focus all their anger on the Bush administration and the right, seemingly unaware that the major threat to liberal values is from the new totalitarianism emanating from radical Islam – which requires liberals also to “support military as well as economic and political efforts to fight it,” Mr. Beinart writes, even when their moral purity is compromised in the effort. In the era of the early Cold War, it was the group of Cold War liberals – centered in the newly created anti-communist group, Americans for Democratic Action – that fought the good fight and mobilized the nation’s support for resistance to Stalin’s aggressive international actions. They urged international economic development combined with military aid to bolster the West against Stalin’s growing threat, in contrast to the new emerging right, with intellectual leaders like James Burnham, who blanched at Kennan’s doctrine of “containment” and posited instead the creation of a new American empire. For them, containment, positing the slow erosion of communism, was moral relativism that accepted tolerating the evil of the Soviet Union.

The strongest portions of Mr. Beinart’s book are his historical accounts of the intra-liberal wars, as the forces of liberal anti-communism joined hands to defeat remnants of the pro-communist wartime Popular Front, symbolized by Henry Wallace’s dangerous attempt to attack Truman from the left while accepting overt communist support. Then, Mr. Beinart asserts, Cold War liberals understood that using American power to thwart totalitarianism abroad was the flip side of using the power of government to promote equality of opportunity and a commitment to civil rights for black Americans at home.

The Cold War liberal consensus came crashing to a halt with the onset of the Vietnam War and the cultural wars of the 1960s.The new left saw the old liberals as its principal enemy.The new group coined the phrase “corporate liberalism” to define what it saw as a failed commitment to the imperialist economic and political system. The choice the new left saw was between fascism and revolution, and it argued that those who favored using American power for good were only serving the nascent fascism lying beneath the surface. While the old generation of muscular liberals understood that the fight against Stalinism served as an impetus for domestic reform, for the new left, as Mr. Beinart writes,”it was the fight against American totalitarianism abroad that served as the impetus for revolution at home.”

The extremism of the new left did not push America toward further progressive social change, Mr. Beinart argues, but led to the demise of any meaningful movements on the left and to the abandonment of liberalism by many who made the drift into neoconservatism and the shift to President Reagan in the 1980s. The noise made by the new left and its academic supporters led to the abandonment of the Democratic Party by much of its former blue-collar base, which refused to give up the old anticommunist consensus. The new liberals led by Mr. McGovern took over the once majority party. But in the process, Mr. Beinart shows, they lost America.

Mr. Beinart’s book is a strong plea that liberals, for the nation’s good, assert a new version of the old liberalism as a meaningful alternative to a flawed conservative hegemony. Conservative thinkers, Mr. Beinart argues, hold to a strong vision of American strength, but also espouse a new doctrine of American infallibility. He argues that these principles contain a willingness to violate other nations’ sovereignty, and under the Bush doctrine, hold to what Mr. Beinart calls a doctrine of preventive war masked under the false label of preemption. Here, Mr. Beinart would have been served well by considering the argument of the Georgetown University professor Robert Lieber, a centrist Democrat like Mr. Beinart who argued persuasively in his book “The American Era: Power and Strategy for the 21st Century” that pre-emption is not such a break from tradition. Instead, he argues, there has been “a long standing willingness to threaten the use of military action without an attack being imminent.” An example of this was President Kennedy’s naval quarantine of Cuba in 1962.

Mr. Beinart’s principal struggle is to provide evidence that any Democrats or liberals exist – aside from him and a few individuals at the Progressive Policy Institute – who are ready to engage in the fight he says is necessary.The one Democrat in Congress who fits his bill is Senator Lieberman, who is being challenged vigorously by the left in his state and stands isolated from the leadership of his own party. Mr.Beinart knows this; he acknowledges at one point that “whatever its failings, the right at least knows that America’s enemies need to be fought.”When he discusses the Reagan administration, he acknowledges that on the critical fight against the Soviets that demanded the establishment of American missiles on Western European soil to counter the Soviet SS-20s, the so-called euromissile struggle that was Moscow’s last major offensive against the West, it was Reagan’s military buildup – opposed by most Democrats and liberals – that led to his being “vindicated by history.” And the liberals united against him did not comprehend, as Reagan did, that it was ideological war in the East, rather than anti-nuke sentiment in the West, that eventually eased the nuclear fears and terror of the 1980s.

Today, our threat is quite different.As Mr. Beinart points out, it comes not from a nonexistent Soviet bloc, but from both rogue states and ideologically motivated Islamic radical cells, from those he calls “Qutb’s children,” referring to the doyen of radical Islamic theology, Salafist Wahhabi totalitarianism, Sayyid Qutb. Jihadists do not need state sponsors, nor are they deterred by the threat of nuclear retaliation, as the Soviets were. In the second half of his book, Mr. Beinart develops a critique of the Bush administration, which he argues has responded incorrectly to the threats at hand by a shortsighted movement at home away from guarding our traditional civil liberties, such as the shadow prison system, CIA secret internments, and the justification for torture.

Bemoaning the movement of many former Democrats to neoconservatism, those who became “Reagan’s children,” Mr. Beinart writes that taking up the challenge of fighting the new totalitarian threat must come only from those who are liberals – an argument that rests a great deal on points already developed by the writer Paul Berman, perhaps our pre-eminent intellectual liberal hawk. Mr. Beinart argues that he and others were wrong to give support to the war in Iraq, although he backhandedly praises the decision of the neo-Reaganites in the Bush camp to work toward the spread of democracy throughout the world, including the Middle East. “The Bush administration has gotten one big thing right,” Mr. Beinart writes. “Tyranny does foster jihad.”But yet he believes that the current administration is incapable of winning the new, necessary fight. Its incompetence has produced “the condition the conservatives have long feared: an America without the will to fight.” But Mr. Beinart knows, nevertheless, that his own favored camp – liberal Democrats – still thinks it has “no enemies more threatening, or more illiberal, than George W. Bush.”

Unlike the Michael Moores and Howard Deans who now lead the liberal Democratic troops, Mr.Beinart makes no such mistake. He sees the threat clearly, and understands that it necessitates a firm and muscular response. While he writes that the Bush administration has made us weaker by making the use of such power appear illegitimate, he does not offer any good reasons why a liberal asserting the use of American power would not get the same negative response from those he is trying to convince. He cautions against the tragedy that would occur if the new McGovernites succeed in their campaign to become the only alternative to the Bush Republicans, and he hopes to avoid the kind of fiasco that might have ruined America had the Henry Wallace left-wing succeeded in 1948.

Mr. Beinart’s hopes seem quixotic. He wants nothing less than a new vision to match that of the old Cold War liberals, who were able to build a “narrative of national greatness for their time.” He wants liberals to support military and economic and political efforts against the new terrorism, even if morally imperfect. He thinks liberals, not conservatives, are more able to pull this off. Conservatives are impatient, while liberals know how to exercise caution, use diplomacy, and convince rogue states to mend their ways.But the New Republic, where Mr. Beinart remains an editor at large, recently ran a cover story arguing compellingly that Iran’s chief cannot be dealt with in any of these traditional ways.

The next few years will show us whether Mr. Beinart’s call takes hold, or whether those for whom he is writing ignore and attack him, leaving only the new Reaganites carrying the torch.

Mr. Radosh, adjunct senior fellow at the Hudson Institute, is author, among other books, of “Divided They Fell: The Demise of the Democratic Party, 1964-1996,” available from the Free Press.