IT'S TEMPTING to have a little sport with President Reagan's continuation of draft registration. He criticized Jimmy Carter for supporting it, and now he's following suit. The stated grounds are pretty flimsy, too: that registration would supposedly give the Pentagon a meaningful six-week jump, rather than the meaningless one week earlier cited, on mobilizing in an emergency.

But the important fact is that Mr. Reagan seems to be moving toward the more sensible position. His main objection to the draft was and remains ideological: short of a major war, the government has no claim to compel the service of the young. But he now is ready to acknowledge that pragmatic considerations have a bearing too. Between the ideological argument against a draft and the countering ideological argument--spread the citizen's burden--for a draft, there is no room for compromise. In dealing with the real world, however, there is.

How is the necessary military manpower to be procured for the possible emergencies and the certain smaller youth populations that lie ahead? Mr. Reagan now leaves open the prospect of some kind of draft, if a fair one can be devised, if the all-volunteer force falls convincingly short. What kind of a "signal" is to be sent to the world in a period of crisis? He will not transmit the kind of everything's-OK signal that the abandonment of draft registration would convey.

Fairly, the anti-draft forces see registration as keeping the door open to a possible draft. Noting that upward of 800,000 men have apparently ignored registration since it was reinstated 18 months ago, they predict a massive government "collision" with a whole generation, leading to a law enforcement "catastrophe."

Nonsense. Non-registration seems to have gotten troublesome only during the year of Mr. Reagan's well-publicized ambivalence: with a president contemplating ending registration, why register? It will be interesting to see how non-registrants respond during the grace period the administration plans, as it had to, to allow.

In any event, as with, say, the tax and driving laws, society demands not that every single violator be prosecuted but that the government show it is serious. This is done not only to catch violators and deter would-be violators but to keep faith with those who voluntarily comply. Mr. Reagan's choice, during the last year, to suspend the enforcement of a valid law was pure whimsy. His decision to enforce registration is not only necessary but right.