Are we safer than we were six years ago? Emphatically not. The risk that we will see American cities go up in smoke has steadily increased since 9/11. The main reason is not the Iraq war or Al Qaeda’s revival. It’s not the surging numbers of America-haters and would-be terrorists, or the most publicized failings of the Bush administration, or the supposed weakness of the Democrats.

Rather, the central threat is the spread of nuclear weapons and bomb-building programs to more countries. The new nuclear threats already include the unstable Pakistani regime, the evil North Korean regime, and (before long, perhaps) the lunatic Iranian regime. More than anything else, such nuclear proliferation increases the risk that terrorists will get and use nukes.

At least as terrifying is the risk that a false alarm will spur someone to launch a multiple-missile attack — perhaps Pakistan against nuclear-armed India or vice versa, perhaps Russia (by mistake) against America — with catastrophic effects on all involved and, ultimately, on the entire human race.

We must work harder to keep nukes out of the hands of terrorists, especially through underfunded efforts such as the Nunn-Lugar program to secure and dismantle nuclear weapons and materials in the former Soviet Union. We must also better secure our borders to keep terrorists from smuggling in nuclear bombs. But such measures are, at best, fingers in the dike.

If a nuclear bomb went off in an American city today, our leaders would probably not know who did it. But at least the list of suspected sources of supply — North Korea, rogue Pakistani generals, loose nukes in Russia, or terrorists who acquire them — would be short. This would increase the chance of identifying and obliterating the supply source. And that is a pretty good deterrent against any rogue state that might want to attack us through terrorist proxies.

But imagine a world in which Algeria, Egypt, Indonesia, Iran, Saudi Arabia, Sudan, and Syria had nukes, with militant Islamists in positions of power in some of those nations, and with Argentina, Brazil, and Japan soon to join the crowd. Such proliferation seems quite likely if current trends continue; experts estimate that more than 40 nations are capable of building nukes. As the number of nuclear nations goes up, the difficulty of identifying the source of any weapon detonated by terrorists in America, or anywhere, will go up exponentially. So will rogue states’ temptation to gamble on handing off a bomb to terrorists.

That’s why Max Kampelman, President Reagan’s arms negotiator, wrote in a New York Times op-ed last year: "At the age of 85, I have never been more worried about the future for my children and grandchildren than I am today."

The best chance of saving our cities, and our way of life, is to stop and then reverse the inexorable rise in the number of nations with nuclear weapons. And the best way to do that is to lead the world toward Ronald Reagan’s vision of abolishing all nuclear weapons, including our own.

Reagan’s dream, shared by then-Soviet President Mikhail Gorbachev, was widely dismissed as either hopelessly naive or a ploy to divert attention from the old boy’s supposed plot to use his missile defense program to develop a nuclear first-strike capability. But over time, a stunning array of the nation’s wise men and women, Democrats and Republicans alike, have endorsed Reagan’s goal — with airtight safeguards against cheating — as our best hope.

They understand that nuclear deterrence, the cornerstone of our security during the Cold War, is increasingly useless against today’s threat from shadowy, nuke-seeking networks of Islamist terrorists around the world.

These wise people include George Shultz, Reagan’s secretary of State; William Perry, President Clinton’s secretary of Defense; Henry Kissinger, President Nixon’s national security adviser; and former Sen. Sam Nunn, who was long the most respected national security expert in Congress. These four, joined by 16 other eminent figures including Kampelman and Thomas Graham Jr., Clinton’s special ambassador for nonproliferation and disarmament, argued in a January 4 Wall Street Journal op-ed for "setting the goal of a world free of nuclear weapons and working energetically on the actions required to achieve that goal."

What moved this bipartisan group — ignored by most in Congress, the administration, and the media — was agreement that the spread of nuclear weapons is the gravest threat to our security and, ultimately, to the human race. They also agreed that the United States can lead the world toward stopping and then rolling back proliferation, in gradual steps, only if the world sees us practicing what we preach. And that means reducing our own arsenal and setting zero nuclear weapons as the goal.

This has not always been my view. I once hoped that we might stop nuclear proliferation cold by invading Iraq, deposing Saddam Hussein, and thus putting the fear of a similar fate into other dictators who might seek to threaten us with nuclear weapons. Indeed, to my regret, I argued in late 2002 that the only effective way to deter rogue regimes from going nuclear was to make a credible threat of pre-emptive military attack, and that the "threat will not be credible unless we can show now that we will attack if necessary to disarm or dethrone Saddam."

This make-an-example-of-Saddam strategy seemed to work on Libya’s Muammar el-Qaddafi. But it has not worked on the leaders of Iran or North Korea, who can see that we are bogged down in Iraq and that we lack the troops and political will to invade them. A bombing campaign could slow Iran’s nuclear program but not stop it — and the costs would be prohibitive. They would include turning the goodwill that many Iranians and others have toward America into hatred.

So what else can we do to reverse proliferation and avert its potentially catastrophic effects? International cooperation — including judicious use of threats and bribes, and strengthening the Nuclear Nonproliferation Treaty — is a maddeningly difficult process. And President Bush long scorned the diplomatic approach. But now he is bribing North Korea, as he should have been doing all along. Perhaps it has dawned on him that diplomacy is about the only option we have left.

The nonproliferation treaty worked surprisingly well from the 1960s until recent years. This was no accident, explained Graham, who served Presidents Ford, Carter, Reagan, and George H.W. Bush as an arms control expert, in a speech earlier this year. "It was rooted in a carefully crafted central bargain. In exchange for a commitment from the non-nuclear weapon states … not to acquire nuclear weapons and to submit to international safeguards to verify compliance with this commitment, the NPT nuclear weapon states … undertook to engage in nuclear disarmament negotiations aimed at the ultimate elimination of their nuclear arsenals. [But] the nuclear weapon states have never really delivered on the disarmament part of this bargain, and in recent years it appears to have been largely abandoned."

We need to renew and take seriously our commitment to seek ultimate elimination of all nuclear weapons. This includes steps that Bush has so far ruled out, such as pledging not to develop a new generation of nuclear weapons or resume nuclear testing. To be sure, few leading Democrats have championed the idea of ending or even reducing reliance on our nuclear arsenal. An honorable exception is Sen. Barack Obama of Illinois, co-sponsor of a bipartisan bill to build on the Shultz-Perry-Kissinger-Nunn group’s proposals.

But most in the administration and in Congress seem to have written off Reagan’s vision as an impossible dream. This reflects a failure of imagination: The steps that we should take toward eventual abolition of nuclear weapons would also greatly reduce the risk of nuclear catastrophe even if the world never gets close to zero. Among those steps, the op-ed asserts, are steep, mutual cuts in the arsenals of all nuclear weapons states; elimination of forward-deployed, short-range nuclear weapons; the highest possible security for all stocks of nuclear weapons, plutonium, and highly enriched uranium around the world; a discontinuation of the use of fissile materials in civil commerce and research facilities; and a U.S.-Russian agreement to reduce the danger of accidental launch by increasing warning time.

The need to increase warning time is especially urgent. As Sam Nunn has argued tirelessly, current policy "risks an Armageddon of our own making" because of the danger of accidental launch. For no good reason, the United States and Russia still keep on 15 minutes alert thousands of nuclear missiles that could devastate both nations in the space of half an hour.

Indeed, Nunn has pointed out, in 1995 Russia mistook a Norwegian test rocket for a submarine-launched American missile and came within two minutes of a retaliatory nuclear attack on the United States. That was a narrow escape. Will we be so lucky the next time?