WASHINGTON (AP) — Veteran Republican Sen. Arlen Specter disclosed plans Tuesday to switch parties, a move intended to boost his chances of winning re-election next year that will also push Democrats closer to a 60-vote filibuster-resistant majority.

“I now find my political philosophy more in line with Democrats than Republicans,” Specter said in a statement posted on a Web site devoted to Pennsylvania politics and confirmed by his office. Several Senate officials said a formal announcement could come later in the day or Wednesday.

Specter, 79 and in his fifth term, is one of a handful of Republican moderates remaining in Congress in a party now dominated by conservatives. Several officials said the White House as well as leaders in both parties had been involved in discussions leading to his move.

With Specter, Democrats would have 59 Senate seats. Al Franken is ahead in a marathon recount in Minnesota, and if he ultimately wins his race against Republican Norm Coleman, he would become the party’s 60th vote. That is the number needed to overcome a filibuster.

Specter faced an extraordinarily difficult re-election challenge in his home state in 2010, having first to confront a challenge from his right in the Republican primary before pivoting to a general election campaign against a Democrat.

“I am unwilling to have my twenty-nine year Senate record judged by the Pennsylvania Republican primary electorate,” he said in the statement.

“I don’t have to say anything to them. They’ve said it to me,” Specter said, when asked in a Capitol corridor about abandoning the GOP.

A senior White House official, speaking on the condition of anonymity because no announcement has yet been made, said at 10:25 a.m. EDT Tuesday President Barack Obama was handed a note while in the Oval Office during his daily economic briefing. The note said: “Specter is announcing he is changing parties.” At 10:32, Obama reached Specter by phone and told him “you have my full support” and that the Democratic Party is “thrilled to have you.”

Specter had publicly acknowledged that to win in 2010, he would need thousands of Pennsylvania voters who switched from Republican to Democrat last year to vote for Obama to flip back to the GOP to cast ballots for him.

As one of the most senior Republicans in the Senate, Specter held powerful positions on the Judiciary and Approporiations panels. It was not clear how Democrats would calculate his seniority in assigning committee perches.

Specter has long been an independent Republican, and he proved it most recently when he became one of only three members of the GOP in Congress to vote for Obama’s economic stimulus legislation.

As recently as late winter, he was asked by a reporter why he had not taken Democrats up on past offers to switch parties.

“Because I am a Republican,” he said at the time.

Associated Press Writer Liz Sidoti contributed to this story.