AT FIRST GLANCE, it may seem that the Carter administration and the House Democratic leadership have vastly improved their Election Day registration bill by agreeing to make the program voluntary. After all, the most persuasive and least partisan objection to the bill has been that it would compel every state to adopt by 1980, at least for federal elections, a new instant-registration system that could easily lead to widespread fraud and confusion at the polls. If the program is now to be optional forever, that criticism has been swept away. States with histories of Election Day problems, such as Rhode Island, Louisiana, Maryland and Illinois, will be free to go on requiring would-be voters to register in advance. States with less turbulent traditions may try out the new approach.

That sounds just fine. . . but wait a minute. If the program is to be optional, why is it needed at all? The states are free to adopt instant-registration or no-registration systems any time. What would the legislation add? Just one thing: money. Federal money, to be precise, through grants for administrative overhead and fraud control and "voter outreach" programs and the like in states that do agree to open their registration rolls on Election Day.

That's why the bill is still alive -- and why we still object to it. We have no quarrel with federal inducements in principle; the carrot is often more effective than the stick. But the idea of federal aid for state and local electoral activities has its own problems. Without careful supervision, "voter outreach" could quickly turn into voter roundups for the benefit of one party, faction or candidate. With federal monitoring, on the other hand, would come federal regulations and bureaucracy -- and equal-opportunity rules for precint workers would not be far behind.

It doesn't help that the federal largesse would go only to willing states. On the contrary, the states most cordial to Election Day registration are likely to be those with the fewest voting problems -- and the least real need for federal aid. One could argue, in fact, that if the aim is to shore up state and local election boards, the greatest help should go to those that don't dare risk instant registration at all. But bolstering election administration seems to be a secondary interest for the Democrats. Their first hope is to get more people to the polls. They ought to try to do that in the customary ways, through good grass-roots organizations, attractive candidates and issues, and strong campaigns.