Both officials spoke on condition of anonymity because Justice Department regulations forbid discussing ongoing investigations particularly so close to an election.
A spokesman for ACORN, the Association of Community Organizations for Reform Now, did not return messages Thursday seeking comment.
Republican accusations about the group were raised during Wednesday's presidential debate between Democrat Barack Obama and GOP candidate John McCain.
ACORN says it has registered 1.3 million young people, minorities and poor and working-class voters. More than 13,000 ACORN workers in 21 states recruited low-income voters, who tend to be Democrats.
But some ACORN employees have been accused of submitting false voter registration forms - including some signed `Mickey Mouse' or other fictitious characters.
Those voter registration cards have become the focus of fraud investigations in Nevada, Connecticut, Missouri and at least five other states. Election officials in Ohio and North Carolina also recently questioned the group's voter forms.
ACORN has said the "vast majority" of its workers are conscientious, but some might have turned in duplicate applications or provided fake information to pad their pay. Workers caught submitting false information have been fired, ACORN officials say.
ACORN says laws in a number of states require it to submit all registration cards it collects even dubious ones, so its workers segregate applications with missing, suspicious or false information and flag them so state election officials can quickly check them further.
House Republicans have been pushing for the Justice Department to investigate ACORN, calling on Attorney General Michael Mukasey to make sure ballots by ineligible or fraudulent voters are not counted on Nov. 4.
The issue also became campaign trail fodder for McCain, who on Wednesday night demanded to know the full extent of Obama's ties with ACORN. McCain said the group could be on the verge of "destroying the fabric of democracy."
Obama denied any significant ties to ACORN and mocked McCain for bringing it up. The Democrat and two other lawyers represented ACORN in 1995 in a lawsuit against the state of Illinois to make voter registration easier, and hired a firm with ties to the group for a massive get-out-the-vote effort during this year's primary.
Earlier this week, Obama said that ACORN was not advising his campaign on voter registration, and the group's registration problems should not be used by the Republicans as an excuse to keep voters from turning out on Election Day.