A three-judge panel in Minnesota has reduced the number of disputed ballots that will determine who won the state’s 2008 Senate race.

In an order issued Friday evening, the judges unanimously ruled that 13 categories out of 19 categories of rejected absentee ballots were not “validly cast.”

The campaign of Republican Norm Coleman estimated that the ruling tossed out about 800 ballots the incumbent hoped would be recounted, leaving about 3,500 still under the court’s consideration.

Coleman is challenging a recount that resulted in him losing re-election to Democrat Al Franken by 225 votes out of 2.9 million cast.

His suit argued that as many as 5,500 rejected absentee ballots should be counted.

Friday’s ruling was an incremental victory for Franken.

His attorney, Marc Elias, said the ruling will “go a long way in shaping the trial from here.”

“It is obviously a large chunk of ballots that have been taken out of play,” Elias said.

The trial is now in its third week and is expected to last several weeks longer.

Coleman’s legal team has presented painstaking evidence, ballot by ballot, in an effort to back up its claim of voter disenfranchisement.

His attorneys have argued that the state should give voters the benefit of the doubt regarding registration procedures and should not hold voters accountable for errors caused by miscommunication by local officials.

In an attempt to accelerate the process, the judges this week invited attorneys for both candidates to discuss the 19 categories of rejected absentee ballots.

Franken’s attorneys argued that all but one category should be rejected, while Coleman’s legal team advocated that the court accept all but four of the 19 categories.