The Soviets are still the main threat, the British government says, affirming its pre-Falklands decision to strengthen its strategic nuclear forces--at enormous cost. But it is a labored argument. Margaret Thatcher's decision is dismal and wrong.

The Soviets, to be sure, are still the main threat: they have the bulk power, the global ambition and the rivalry with the United States to warrant continuing concern by the democracies and the countries sheltered by them. The West must exercise nuclear prudence--let us set aside the difficulty of determining what it is.

But why must the Brits stay in the nuclear game?

There has not been a better moment in years for a British government to acknowledge that although the Soviets are the main threat in an ultimate cosmic way, something else more relevant to British interests and capabilities is the main threat in the common earthbound way in which nations live from day to day and year to year.

A British government so minded could have granted that although the Soviets are inveterate pot-stirrers, they were not responsible for Argentina's grab of the Falklands. The British themselves, by helping to arm Argentina even while frustrating its national obsession, were far more responsible. And only in a backstage permissive arms supplier's way, one in which the United States is much more heavily implicated on the Israeli side, can the Soviet Union be held to account for the maelstrom in Lebanon.

In both of those wars, as in most other local wars that you can think of, the threat or the cause or the trigger did not really consist of Soviet machinations, least of all of Soviet ideas, although the Soviets are often an aggravating factor. It consisted of an unresolved local grievance that, instead of being treated by political or diplomatic or economic means, was allowed to fester until it exploded.

"We look around the world," Ronald Reagan said in his recent United Nations speech attacking the Kremlin, "and see rampant conflict and aggression. There are many sources of this conflict--expansionist ambitions, local rivalries, the striving to obtain justice and security. We must all work to resolve such discords by peaceful means and to prevent them from escalation."

A reversion to conventional-power status could give Britain the additional resources, not to speak of (nor to exaggerate) the moral authority, to make a significantly greater contribution to "resolving such discords."

What has Britain gotten from its nuclear status? Argentina was not intimidated by it in the South Atlantic, any more than the Palestinians have been intimidated by Israel's apparent near-nuclear status in the Middle East. Neither Britain nor Israel invoked their respective nuclear capacities. Going nuclear is, thank heavens, not considered acceptable and relevant in the world's virtually continuous round of "little" wars.

Why, then, are the British making a huge new nuclear investment that will divert funds from the very programs that have put back a glint in their eye and that promise to be more useful and cost-efficient in protecting British interests than any new Trident missile system ever will be? And British interests, it is worth saying, are generally American interests, notwithstanding the heartburn Thatcher gave Washington in the Falklands.

No doubt the explanation lies ultimately in the sense of control of one's own destiny, and in the sense of playing in the global big leagues, that is thought to be conferred by nuclear status.

I am an unrepentant great-power chauvinist: one who feels that the world would be a marginally safer place if only the United States and the Soviet Union possessed nuclear weapons. I regret that the British could not have seen their defense choice, now as long ago, another way.

Their nuclear armory adds very little to their security that is not bestowed by their American connection. Their additional conventional power, in and beyond NATO, could amount to a good deal. Imagine the benefits to the West if the British had not withdrawn their steadying presence from the Persian Gulf 10 years ago. By upping their nuclear ante now, they virtually ensure a further drawdown in usable Western power. Their nuclear itch serves them and us ill.