Contrary to Clemenceau--or was it Gore Vidal?--conservatives are not the stupid party. It's merely that from time to time conservative administrations seize on the opposition's worst ideas, adopt them as their own, and seem stupid.

Case in point: the Reagan administration's current passion to enforce the Carter Draft Registration Act.

Very shortly, within a matter of days or weeks, the Department of Justice is going to enter the twisting tunnel of prosecuting young American males between the ages of 18 and 22 who have failed to register for a draft we are assured will never take place without another act of Congress. If all goes well for the prosecution, these registration-evaders will be convicted and jailed under terms of a law passed as an election-year cosmetic by the Carter administration--a law that, if it offers those jailed any comfort, was vigorously opposed by Ronald Reagan when he campaigned for the presidency.

Thus, Jimmy Carter's bad law--pushed through Congress during the post-Afghanistan period when the then-incumbent was striking various election-year poses of "toughness" toward the Russians--will become Ronald Reagan's bad law, in the same way that Lyndon Johnson's "limited" war became Richard Nixon's. If history is any guide, we may then expect some of the same people who supported Carter against Reagan to take to the streets and otherwise protest the Reagan administration's execution of a policy initiated by its predecessor.

How did an administration intent on overturning just about every other policy and program endorsed by the Carter White House get itself into this bind? Like a booby trap, the Draft Registration Act lay waiting in the West Wing when Ronald Reagan took office. Given his personal instinct and public statements regarding its efficacy as a way to strengthen the armed forces, the law could and should have been left dormant. Instead, the new administration, encouraged by empire-building Pentagon bureaucrats--yes, Mr. President, they run loose in the Defense Department, just as they do at Health and Human Services--chose to leave the booby trap in place. Now it is about to be sprung.

True, proponents of registration have their side of the story. First, they argue that the law is painless because it doesn't draft anyone; second, that we need it in order to shorten the period of readiness for a full-scale draft in case one is needed (though estimates on how much time will actually be saved by pre-registration vary from Pentagon bureaucrat to Pentagon bureaucrat); finally, that whether the law happens to be good or bad, it's the law, by God, and has to be enforced--in the same way that Johnson's disastrous war policy, regardless of its origin or effect, had to be carried on by his successor.

For a conservative administration, these are tempting arguments, running the buzzword gamut, as they do, from national defense to respect-for-the-law. But that's the way it always is with booby traps--if they didn't look tempting, or at least safe, they wouldn't serve their purpose.

Not to imply that the Carter administration passed the registration bill in order to trap its successor. On the contrary, the law's political purpose was to help give Jimmy Carter the "tough" national defense image his polls showed he needed to win the election. It went hand-in-hand with that "secret" bomber the Pentagon began talking up when the campaign moved into high gear.

Indeed, the real inspiration behind the Carter administration's pushing the draft registration bill can be discerned by how little, rather than how much, it does. If advance registration really saves time, why is the bill limited to 18- to 22- year-olds? Why aren't potential draftees up to age 26, or even 30, included? Call me cynical--I've witnessed a fair number of presidential campaigns--but I can almost hear the political give-and-take that went into shaping an election-year bill that could cover the national defense line without shaking up too many voting parents and potential draftees.

So it is that unless the administration reverses its present course, able-bodied 23-year-old American males of fighting age will go untouched by a law we're told is so vital to the nation's interests that it justifies jailing 18- to-22-year-olds. This was precisely the sort of bureaucratic hit-and-miss technique that characterized the inequitable draft law of the Vietnam War years.

What should the president do? Well, a new beginning, to coin a phrase, wouldn't be a bad idea--in the form of a comprehensive study by the White House and Congress of the country's legitimate military manpower needs. Meanwhile, enforcement of the Carter Draft Registration Act should be put on ice.

Impractical at this late date? Not at all, considering the alternative--which is that the Reagan administration will soon be asking for prison terms of up to five years for young Americans who refuse to register in peacetime, thereby implementing a law enacted by the same president who amnestied other Americans who refused to serve in wartime.

For Jimmy Carter's administration to have pursued such a course, had he been reelected, would have been an act of moral hypocrisy; for Ronald Reagan's administration, it will be, to put the most favorable light on it, an act of political stupidity.