PARIS -- Back in the dim, dark days when American conservatives not only preached the cleansing redemption of balanced budgets but actually lived by that credo, tax cuts were a liberal issue. It took Ronald Reagan's conversion to supply-side economics to plant the tax-cut banner firmly on the right.

Something similar may be occurring on nuclear disarmament, another issue that has long been identified with the left but which Reagan is appropriating as his own and as a conservative cause. His continuing endorsements of the need to abolish all nuclear weapons go far beyond the point of being simple political or rhetorical devices.

To the dismay of many of his conservative supporters and the chagrin of liberals, Reagan's calls for nuclear disarmament are beginning to form a political program that contains a potent emotional force for electorates at home and in Europe. That force could drag all other western politicians along behind Reagan on this issue, just as they have been swept up in his wake on tax cuts.

This will be particularly true if Soviet leader Mikhail Gorbachev cooperates with the American idea of a high-profile, buddy-buddy Thanksgiving summit in the United States. It is hard to see why he would cooperate with this treacly notion except for precisely this opportunity.

Out of this confusion along the ideological spectrum could come a better result, however. Those who are left uneasy by Reagan's approach to nuclear disarmament must now focus on and articulate the realistic proposition that the world is better off having (some) nuclear weapons. Minimal deterrence makes sense not only strategically, but also politically for liberals trying to counter Reagan the peacenik.

Instead of seeking to negotiate the impossible dream of a nuclear-free world, the United States and the Soviet Union should be attempting to identify and achieve the minimum nuclear force each side needs to deter the other from attacking. This is a better guarantee for peace.

Thus far a strategy based on minimal deterrence seems to hold little attraction for Reagan. He is remarkably tenacious in his descriptions of a world in which the United States is protected either by his Strategic Defense Initiative space shield, which is to render offensive nuclear weapons obsolete, or by a negotiated renunciation of the nuclear balance of terror with the Soviet Union.

He returned to it again this week in an interview in The Washington Times, in which he said a denuclearized world would be a safer place. He explained that the disaster at the Chernobyl nuclear plant must have given Soviet leaders "some second thoughts about an exchange of nuclear weapons."

His remarks hint that Reagan now believes that Gorbachev is serious about accepting the doctrine of "reasonable sufficiency," the rough Soviet equivalent of minimal deterrence. This is an opening that should not be allowed to get lost in the shuffle of an overly ambitious summit.

If Reagan and Gorbachev could come out of their third conference agreeing to a 50 percent reduction in strategic weapons as part of a clearly identified commitment to reduce their nuclear arsenals ultimately to a few hundred warheads on each side, stability will be significantly increased.

For Reagan's nuclear-free vision contains two major fallacies. One is that we can negotiate our way to a situation of conventional deterrence in Europe. History, and logic, show otherwise. Germany in 1939-40 and Israel in 1967 are only two examples of dedicated and confident nations launching war against numerically superior adversaries.

Second is the idea that SDI would ever give the United States enough confidence to do away with offensive nuclear weapons. Whatever the statistical chance that one or two Soviet warheads would get through, it would be too high for rational decision-makers to take the risk to expose America to that level of damage.

This point has just been underscored by published accounts of the reunion in March of John F. Kennedy's principal advisers on the Cuban missile crisis of 1962. What is clear from those accounts and private remarks by some of those who were present at the Hawk's Cay, Fla., meeting is that the risk of even one Soviet nuclear warhead getting through American defenses was seen as having presented too grave a risk to justify a military attack on the Soviet missiles in Cuba.

Minimal deterrence worked then. After the arms-building binges on both sides over the past 25 years are undone, it can work again.