IT'S NOT CLEAR whom President Carter had in mind when he told the United Auto Workers the other day that "some powerful special interests are trying to kill the electoral reform bill, because they don't want working people to register and to vote." That formulation may serve the President's interest - and perhaps his party's - in bringing about instant, election-day voter registration. But one need not be a "special interest" in order to see grave defects in the bill. To sum up our own view in Mr. Carter's terms, we do want working people and others to register and vote - but not necessarily on the same day.

The bill's wrongheadedness starts with its premise that pre-registration is a major barrier to voting. That have been greatly eased since 1960 - the percentage of voting-age Americans who turn out in presidential elections has been dropping anyway. The primary causes of the decline are demographic changes, public disenchantment and apathy - forces that can't be countered by a law. While simplifying pre-registration - by using a postcard system, for example - is a good idea in itself, it does not necessarily lead to larger turnouts at the polls. Even abolishing pre-registration may affect the turnout less than the nature of a given campaign. Last November, turnouts were a few percentage points above 1972 levels in the four states with instant registration. But they were also higher in most Southern states, where pre-registration is still required.

It's generally assumed that larger turnouts would help the Democrats, which is why partisan lines are drawn so sharply on this bill. The basic question, though, is whether democracy as well as Democrats would be well served by making election-day registration available in every precinct in the land. An impressive array of state and local election officials, among others, say no. They predict widespread fraud if they can no longer obtain signature cards and verify addresses of all potential voters before election day. Requiring voters to show IDs and sign an affidavits at the polling place may deter fraud in Minnesota and other states where elections are generally scandal-free. In areas with more turbulent traditions, though, stronger precautions have proven desirable - as Rhode Island's secretary of state said in Senate testimony excerpted For the Record on this page.

The administration's bill presents other problems, too. IT would compel most states to rewrite their election laws in short order, and to train many new precinct workers to process instant registrations. It would trample on the tradition of state governance of state and local elections. States would have to either extend instant registration across the board or suffer the cost and confusion of running elections under two different sets of rules. Finally, the federal grants for administration and "voter outreach" strike us as virtually impossible to police with out bureaucratic controls so elaborate that the states will rebel and the Federal Election Commission will collapse.

All in all, the more we study this proposal, the worse it looks. We have no quarrel with instant registration, or no registration, where the integrity of elections is not jeopardized thereby. But the states ought to make that judgment for themselves. We see no current abuses so flagrant, and no potential benefits so great, as to justify the dangers this program would open up and the disruption it would cause. If the Democrats want to get more voters to the polls, they should try to do so in the time-honored way: through good political organization, a sound choice of issues, strong candidaates and vigorous campaigns.