IS THE Justice Department discriminating against blacks by bringing vote fraud prosecutions against black local officials in the South but not against whites? That issue is raised by recent federal cases brought in Alabama. In the first to come to trial, three Perry County black political organizers were acquitted July 5 of absentee ballot violations. In other cases, five Greene County defendants, including a black mayor and a white county employee, are being prosecuted in Birmingham on similar charges; the mayor's case was declared a mistrial on Wednesday.

These cases arose in rural Black Belt counties where most of the residents are black and where, for many years, only whites were allowed to vote. After the passage of the Voting Rights Act, a lively and evidently bitter political competition arose there, with voters and politicians split almost, but not quite entirely, on racial lines. At stake are local government jobs and the control of law enforcement agencies. Typically the decisive races are in the Democratic primary, and typically both sides organize massive absentee voter drives to maximize their votes. A great many people -- in some cases more than the current population -- have migrated out of these rural counties in the last three decades, and it seems likely that both sides have been seeking votes of people who once lived in the county but haven't spent much time there recently.

The intervention by federal prosecutors on the side of the mostly white political factions has produced some odd results: black political leaders who once sought federal action now question it, and seek the support of Gov. George Wallace. Alabama black political leaders concede that vote fraud should be prosecuted. But they argue that federal enforcement has been one-sided and that the evidence in these cases was flimsy. The acquittal in the Perry County case goes some way toward supporting their argument, although there are cases in which the evidence is strong enough to justify a prosecution but not enough to persuade a jury to convict.

At this distance it's hard to assess the worthiness of these cases. The record does show that the federal government has brought vote fraud cases in big jurisdictions and small, against black officials and in counties where almost no blacks live. Certainly there are occasions when the local political process is corrupted and federal intervention is the only way to eradicate and punish fraud. But the government must also be alert to the dangers of intervening too clumsily in local political struggles. In the Alabama cases, for example, it's alleged that brusque FBI questioning and the hauling of witnesses before a grand jury in distant Mobile had a chilling effect on elderly rural black voters who remember al too well the days of disenfranchisement and intimidation.

There doesn't appear to be any national administration policy of trying to intimidate black voters by bringing vote fraud cases. But it's possible, and a promised House subcommittee hearing may cast light on whether these cases have been handled as they should have been.