Franken opened up a slight lead on the fourth day of a state Canvassing Board meeting to decide the fate of hundreds of disputed ballots.
The change was notable because Coleman led Franken in election night returns and also held a 188-vote lead before the board took up challenged ballots. But its significance was limited, with the possibility the lead could change again before the long recount ends.
The board had several hundred remaining challenges to resolve, with a goal of doing so by Friday. Both Coleman and Franken are also waiting to see how much they gain from some 5,000 challenges that they withdrew, and the board won't allocate those until Monday.
The outcome of the recount also depends on an estimated 1,600 absentee ballots that were improperly rejected. The state Supreme Court ruled Thursday that those ballots must be counted, and set a Dec. 31 deadline for counties to work with the candidates to identify and count them.
The high court ruling virtually guaranteed that the recount would sprawl into the new year. With Congress set to convene Jan. 6, Gov. Tim Pawlenty said his staff was researching the possibility of a temporary appointment.
But Pawlenty said it was unlikely he would do so because he expected the recount would be resolved by then.
The ballot that put Franken in the lead came from Rochester, where a voter's mark for Franken filled not just his oval but a good chunk of territory next to it. A challenge from the Coleman campaign was rejected.
Once in the lead, Franken was certain to expand it because almost all of the remaining challenges before the board were from Coleman -- and the board was rejecting most challenges. By late morning, he led by 66 votes.
Coleman spokesman Mark Drake said Franken's lead was temporary. "We encourage everyone to just hang on until the process is finished," Drake said in a statement. "When it is finished, Norm Coleman will still lead, and we believe, be re-elected to the United States Senate."
Before the five-member canvassing board began reviewing challenges Friday, it rejected a request from the Coleman campaign to disqualify hundreds of ballots that the campaign argued were duplicates and had been counted twice.
G. Barry Anderson, a Supreme Court justice serving on the board, said the issue was not the board's to decide.
"While I think there is a serious issue here, the location, extent and remedy lie elsewhere," Anderson said.
Coleman's campaign on Friday released a letter to Franken, proposing that the issue of duplicate ballots be handled in each county as part of the process to identify erroneously rejected absentees.
Franken's campaign did not immediately respond.