In the 13 years since the Cold War ended, the U.S. nuclear weapons arsenal, designed to deter Soviet attack by threatening massive retaliation, has become increasingly ill-suited to deterring the more diversified -- but still deadly -- threats that face us. Deterring rogue states and terrorist groups from using weapons of mass destruction is still possible, but only if we modernize our nuclear forces. Transformation of these capabilities has hardly begun, though, and our risks are increasing by the day.

To be effective deterrents in the future, our nuclear weapons must have greatly increased accuracy, reduced yields, specialized capabilities (such as deep earth penetration) and tailored effects (such as ability to neutralize chemical-biological agents). The administration has proposed urgent steps to gain information in these areas, but for the past two years these initiatives have been halted or slowed by those who believe U.S. national strategy should focus on nonproliferation and play down nuclear weapons. Those who share these views advance the following four arguments to support their case.

* New low-yield, accurate nuclear weapons would reduce the nuclear threshold and blur the distinction between conventional and nuclear weapons, thus making their use more likely.

This statement is both illogical and wrong. Our primary objective is deterrence, and this lies only in our adversaries' minds. The leadership of a rogue state (e.g., North Korea) might believe we would not use existing nuclear weapons (with hundreds of kilotons' yield) to defeat threatening nuclear weapons in a hardened facility, because that could also kill or injure thousands of noncombatants. Thus, in the absence of new low-yield weapons, our deterrence would be lessened, the adversary's provocations would proceed, and the use of nuclear weapons would be more likely. By continuing with our ill-suited stockpile we would have lowered the nuclear threshold.

But if we build and test new nuclear weapons, train our armed forces in their employment, announce national policies that include their possible use, and develop a national consensus supporting such use if necessary, our adversaries will be deterred and will modify their behavior. By building new low-yield nuclear weapons we will have raised the nuclear threshold. Our adversaries must be convinced that our nuclear weapons have the precise capability to destroy their high-value assets and that we have the will to use them.

* New low-yield nuclear weapons are different from those that kept America safe during the Cold War. Those older megaton weapons were useful only for deterrence. These new ones are obviously for war-fighting.

Again, incorrect. Our Cold War arsenal deterred because it was "tuned" to our adversaries, their value systems and the threats they posed. These key determinants have changed drastically. Deterrence, not war-fighting, is still our objective, and we must change our nuclear arsenal to be effective against future adversaries and their value systems. Low-yield weapons are not all that "usable." U.S. and Soviet Cold War arsenals included many thousands of low-yield weapons, yet none were ever used, even though there were many crises.

* Proliferation of weapons of mass destruction is the world's greatest threat; we should multiply our efforts to persuade all nations to forgo them. How can we do this when we are launching new nuclear weapons programs?

There is no inconsistency whatever between these two actions. We are one of five internationally agreed "nuclear weapon states." As such, we are obligated to maintain secure, reliable and effective nuclear weapons. No other nation has the global responsibilities the United States bears, and we must take the actions needed to meet them -- particularly those involving deterrence.

As for nonproliferation, it is a cornerstone of U.S. foreign policy. We are the world's leader in advancing it. We have created more initiatives to further it, spent more money to support it and done more to strengthen it than any other state. We will continue to expand this nonproliferation campaign, but in parallel we must transform our nuclear weapons to regain essential deterrence capabilities.

* Development of new nuclear weapons would violate our obligation under Article VI of the Nonproliferation Treaty, which pledges all states to work toward nuclear disarmament.

This statement incorrectly confuses short-term actions with long-term goals. Article VI does not prevent any nuclear weapon state from developing new nuclear weapons. The complete article states: "Each of the Parties to the Treaty undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a Treaty on general and complete disarmament under strict and effective international control." We have met these obligations -- in spades. We have ended the arms race with the Soviet Union, reduced our nuclear weapons stockpile by many thousands, signed the Moscow Treaty to reduce it by many more thousands, dismantled entire classes of nuclear weapons and taken hundreds of other actions to reduce nuclear weapons activities worldwide.

But in a dangerous world, with many states and organizations committed to acquiring and using nuclear weapons, it would be unwise for the United States not to make our nuclear deterrent force more effective. Actions to achieve this, while simultaneously greatly reducing the number and yield of our nuclear weapons, are fully in accord with the treaty.

We are at a critical point regarding the future role of nuclear weapons in national security. Dependence on the aging stockpile from a former era will not serve. We should move rapidly with the administration's modest investigative initiatives to gain information needed for future decisions.

The writer is a retired Navy vice admiral and former director of the Defense Nuclear Agency.