The frequent presidential debates have not so much brought out the differences among the candidates as their similarities.

No profiles in courage have been sighted; pandering is much in view. The four front-runners have all kowtowed to the implacable Miami Cubans in the matter of Elian Gonzalez. On the question of the Confederate battle flag over the South Carolina capitol, the Republicans have wrapped themselves in it and offered incense to states' rights, the elastic alibi that kept Jim Crow in charge of race relations for a century after emancipation. Bill Bradley and Al Gore, without a prayer in South Carolina come November, vehemently oppose "a symbol of racism."

No one's style has changed much through their many encounters. Gore, out of earth tones and back in blue serge, is still the uptight scoutmaster, preachy and strident. Bradley, who is an uneven performer--he was disastrously short and snappish in a previous New Hampshire debate--was back on his game in Iowa Monday night. He is taxed with being aloof, but his tone is much more conversational than Gore's.

He did something of a double whammy during the hour devoted to race relations. He told Gore that he should stroll down the hall and ask President Clinton to sign an executive order outlawing "racial profiling," an offensive practice of singling out people of certain races for police attention. It gave him a chance to look like Mr. Direct Action and helped him highlight Gore's sticky relations with Clinton.

On the other side, neither John McCain nor George W. Bush expects to shine for the studio cameras. Bush never troubles to explain himself--his preferred forum is the mobbed cafe or high school gym, where he can hug voters and schmooze with them. And McCain hasn't elbowed his way to where he is by being a policy wonk. He's a little vague when it comes to the fine print in his tax proposals. He's hard on Bush's heels because of a best-selling book, "Faith of My Fathers" and because he seduces reporters on his "Straight Talk" campaign bus with his beguilingly indiscreet confidences.

A disproportionate amount of debate time has gone to gays in the military and a tax on the Internet. No passionate convictions have been uncovered. No tempers have been irretrievably lost. The discussion has been shaped largely by the questions of the moderators, but someone who really wanted to push his agenda or float a new idea can find a way to work it in. Foreign policy gets no time to speak of.

One issue that has not arisen, strikingly, is one that should transcend all others, nuclear weapons. The Republicans' smothering of the Comprehensive Test Ban Treaty in the Senate has not been mentioned. Nuclear matters are discussed only in the context of a nuclear missile defense system, Ronald Reagan's weird legacy, now embraced by all.

This week, it failed a test over the Pacific. Will the failure cause the president to cancel the multibillion-dollar experiment--with its incalculable effects on arms control, relations with Russia, the ABM treaty and proliferation? The country should care.

In the January issue of Harper's magazine, Jonathan Schell reminds us in somber and irrefutable terms that a refusal to talk about survival will not make 31,000 nuclear weapons still in the world go away. For the new century, it is, he writes, the nuclear question that is "the deepest of the questions that need answering."

The new abolitionists, a small band in our midst, advocate getting rid of the means of exterminating humankind. They have been ignored.

Schell draws an eerie parallel between the dawn of the 20th century and today. His starting point is the 1891 publication of Joseph Conrad's "Heart of Darkness," which prefigured the violence and exterminationist tendencies of the last hundred years. "Conrad wrote in the heyday of a liberal civilization that had seemed to spread steadily and grow stronger for most of the nineteenth century. Its articles of faith were that science and technology were the sources of a prosperity without limits; that the free market would spread the new abundance across the boundaries and nations; that liberty and democracy . . . were gaining ground almost everywhere."

Sound familiar? Let's not hear that a campaign is no place to talk about doomsday.

It's the best place. In 1964, the nuclear bomb was the most powerful theme of the contest between Lyndon Johnson and Barry Goldwater. "Whose finger do you want on the button?" Johnson would shout. An overwhelming number of Americans, who shuddered at Goldwater's fascination with nukes that were the size of fountain pens, chose Johnson.

The survival of mankind is surely a worthy topic. It seems more relevant than, say, a tax on the Internet.