ANCHORAGE, Alaska (AP) — U.S. Sen. Ted Stevens, the longest-serving Republican in Senate history, filed for re-election Thursday.

The 84-year-old Stevens, who also is under a federal investigation, filed his paperwork at the state elections office in Anchorage.

Stevens is the most powerful elected official in Alaska state history.

He was appointed to the Senate in 1968, won election two years later in a special election and has been re-elected six times.

Federal authorities are investigating the senator's ties to a corrupt oil services contractor who helped remodel Stevens' official residence in Girdwood. Stevens hasn't been charged, and said he paid all bills presented to him.

Though positions on Senate committees controlling the country's purse strings, Stevens has delivered billions of dollars to Alaska, a state rich in land but poor in infrastructure.

Grateful constituents named the largest airport in the state after him, but his legacy was tarnished last year by a federal investigation that included a raid by the FBI and the IRS on his home in Girdwood, a ski-resort community on Anchorage's southern edge.

Bill Allen, the former head of VECO Corp., an oil field service company, who has pleaded guilty to bribing Alaska state legislators, testified in trials that he oversaw extensive renovations at the home of Stevens and sent VECO employees to work on it.

Stevens has not been charged and has said he paid all bills he received for the remodeling project.

Stevens has maintained a policy of not discussing pending investigations. He said he did not want to be perceived as trying to influence the investigation.

Democrats believe the investigation could make Stevens vulnerable in this year's election. Top party officials are encouraging Anchorage Mayor Mark Begich to challenge Stevens, but Begich has not yet announced a decision.