Sen. Arlen Specter (R-Pa.) is set to announce in early April that he will seek a sixth term in the Senate, though he is not up for reelection until 2010, his office said Monday.

Specter, 77, who has often butted heads with the Bush administration, narrowly survived a primary challenge from conservative former congressman and current president of the Club for Growth Pat Toomey.

Because of the lessons learned from that close race, Specter is announcing his reelection bid early as a “preemptive move” in an effort to raise enough money to scare off potential challengers, according to Terry Madonna, a pollster and analyst at Franklin and Marshall College in Lancaster.

“He’s obviously trying to not set off a scramble … within his own party,” Madonna said. “And … he’s sending a message to conservatives who want to do battle with him.”

Toomey, who is rumored to be considering a run for Pennsylvania governor, ran a hard race at the moderate Specter, running from his right and forcing the senior senator to seek support from a White House he has often rebuffed.

According to the most recent Keystone Poll, Specter has the highest approval rating of any politician in the state, Madonna said.