The presidential campaign of Sen. Barack Obama (D-Ill.) asked the Justice Department on Friday to allow an existing special prosecutor to probe the possible collaboration between the Bush administration and the presidential campaign of Sen. John McCain (R-Ariz.) in generating what Obama aides charge are spurious allegations and investigations of voter fraud.

In the letter, and in a conference call, Obama officials charged that government leaks about FBI investigations into possible voter fraud point to a potential collaboration between the administration and the campaign.

The letter is to Attorney General Michael Mukasey and Special Prosecutor Nora Dannehy, who is looking into possible political motives in the firing of U.S. attorneys earlier in the administration. Allegations have been made that some of the U.S. attorneys were fired because they had failed to sufficiently investigate voter fraud. Many Democrats suspect the allegations and the firings were part of a politically motivated effort to stymie voter registration.

The McCain campaign has charged that the groups are engaging in fraud by illegally registering voters. McCain and his aides say such activities, particularly those of the activist group Association of Community Organizations for Reform Now, are casting a pall over the election. McCain’s team also has linked the group to Obama’s campaign.