Breaux said questions about whether he is legally a Louisiana resident would keep him from "running on the issues instead of the law," The New Orleans Times-Picayune reported.
Gov. Kathleen Blanco, battered by criticism of her performance in the aftermath of Hurricane Katrina, announced a few weeks ago that she would not seek re-election. Breaux became a candidate almost immediately, but because he moved to the Washington area after leaving the Senate, he was unsure if he could meet Louisiana's residency requirements.
Breaux asked state Attorney General Charles Foti to give a legal opinion on his eligibility but Foti refused. That left the issue to be resolved in a court fight.
At least two Democratic candidates have already declared. Under the Louisiana system, all candidates from any party run against each other, with the two top vote-getters competing in a runoff if no one gets more than 50 percent.