Nothing is more heart-rending than the cry of a disenchanted true believer in the Ronald Reagan of yesteryear -- if you counted yourself among them. But if you were not of that persuasion, there is also quite a lot that is heartening in an article in the year-end issue of Foreign Affairs by Norman Podhoretz.

Podhoretz is the prestigious editor of Commentary magazine, the literary home port of neoconservatism. This is a cult largely composed of prominent, fallen-away Democrats who thought back in 1980, as Podhoretz puts it, that they had discovered in Ronald Reagan (a former Democrat) "a more legitimate heir to the mainstream Democratic tradition in foreign policy -- the commitment to containment [of communism] running from Truman through Kennedy, Johnson and the late Sen. Henry M. Jackson."

And Podhoretz was pleased with the original thrust of Reagan policy: the avoidance of arms-control negotiations that might have "jeopardized" the necessary buildup to redress the U.S.- Soviet balance of military power. He liked the way Reagan went about rekindling America's patriotic spirit in the interest of restoring confidence "in the utility of military force as an instrument of worthy political purposes." He applauded Reagan's reinstitution of the East-West ideological conflict as the centerpiece of U.S. policy concern -- in contrast to the preoccupations of his predecessors with geopolitical power- balancing or great-power rivalry.

So what's his gripe? It is that the pure conservatism of Ronald Reagan, private citizen, has given way to, God help us, the practical political imperatives imposed on a president. "D,etente," as practiced by Nixon and Henry Kissinger, never lived up to Podhoretz's hopes.

Now, it is Podhoretz's deepest anxiety that in his second term, Reagan, "overwhelmed by the pressures of the political present, and perhaps lured by seductive fantasies of what historians in the future might say of him as a peacemaker . . . seems ready to embrace the course of d,etente wholeheartedly as his own."

Warning signs, as Podhoretz perceives them, are everywhere in the record. Economic pressures are a key part of the "linkage" that is, in turn, essential to "hard-headed" d,etente. "Yet the enormous irony is that in the economic sphere Ronald Reagan, the great critic of d,etente . . . did not even measure up to the standards of toughness required by Mr. Nixon's theory." Having promised "linkage," he unlinked Jimmy Carter's grain embargo from the grand scheme of U.S.-Soviet relations. He caved in on the European natural-gas pipeline to the Soviet Union out of some misguided concern for "alliance solidarity."

Reagan hailed the Afghanistan "freedom fighters," but did not do nearly enough to help them on a scale "large enough to make a decisive difference," Podhoretz complains. Reagan is excused for not "toppling" the Marxist Sandinista regime in Nicaragua -- but only because Congress got in his way. But Reagan was not even as bold as John Foster Dulles (for whom Podhoretz has a low regard as a risk-taker) in Lebanon.

Podhoretz grants that under Reagan, "America was (his emphasis) back -- in at least the sense that it would no longer passively acquiesce in the achievement of an irreversible military superiority by the Soviet Union." But he fears it has not been prepared, as it was only 20 years earlier under Kennedy, to "pay any price, bear any burden, meet any hardship, support any friend . . ."

The truth is, of course, that Kennedy himself wasn't prepared to live by that inaugural rhetoric three months later when he fatally scaled down the American role in the Bay of Pigs. There lies the real flaw in the Podhoretz analysis. His dream is not of a different Democratic Party but of a different day when the United States had overwhelming military superiority, a near-monopoly in nuclear weapons and abundant economic resources.

What Podhoretz seems to be deploring is that Reagan, as president, has come to recognize the necessity as a practical matter of reconciling his old ideology with the new realities. Podhoretz sees Reagan moving not only toward arms control but maybe even broader agreements with the Soviets on the rules of East-West engagement.

He sees the president headed toward a deal in Central America, accepting a communist Nicaragua in exchange for something rather like the prescriptions of the Contadora countries. If he should "move in this direction, he will cruelly disappoint those of us who once hoped that he might lead the Republican Party into assuming a responsibility for resisting Soviet imperialism that he himself had so often and justifiably attacked the Democrats for no longer wishing to carry."

And so he might. But that would not be too heavy a price to pay for those of us who believe that if Ronald Reagan should move in the direction Podhoretz so deplores, he would be on the right track.