WASHINGTON  Al Franken, the comedian turned politician, won a potentially decisive court ruling on Tuesday in his bid to replace Norm Coleman, a Minnesota Republican trying to hold on to his Senate seat.

A three-judge panel ruled that only 400 absentee ballots  far fewer than Mr. Coleman had sought  should be examined for possible counting. If the ruling stands, it could be devastating for Mr. Coleman, who trailed his Democratic challenger by 225 votes out of some 2.9 million cast and had hoped that nearly 1,400 absentee ballots might be recounted.

Even if the results put Mr. Coleman further in the hole, as expected, he could fight on, before the Minnesota Supreme Court or perhaps in the federal courts. His lawyer said Mr. Coleman had not given up.

After seven weeks of deliberations, the court said it would decide which of the 400 ballots would be counted in open court by next Tuesday.