CNN

WASHINGTON (CNN) – Veteran Pennsylvania Sen. Arlen Specter told colleagues Tuesday he intends to switch from the Republican to the Democratic party.

A Specter party switch would give Democrats a filibuster-proof Senate majority of 60 seats if Al Franken holds his current lead in the disputed Minnesota Senate race.

"Since my election in 1980, as part of the Reagan Big Tent, the Republican Party has moved far to the right," Specter said in a written statement posted by his office on the Web site PoliticsPA.com.

"Last year, more than 200,000 Republicans in Pennsylvania changed their registration to become Democrats. I now find my political philosophy more in line with Democrats than Republicans."

Specter, a five-term Senate veteran, was greeted by a loud, sustained round of applause by dozens of constituents outside his Washington office shortly after the news broke.

"I don't have to say anything to them," a smiling Specter said. "They've said it to me."

President Barack Obama called Specter shortly after learning the news during his daily economic briefing in the Oval Office Tuesday morning, according to a senior administration official.

"You have my full support and we're thrilled to have you," Obama told Specter.

Jubilant Senate Democrats also welcomed the news.

"Sen. Specter and I have had a long dialogue about his place in an evolving Republican party," Senate Majority Leader Harry Reid, D-Nevada, said in a written statement.

"We have not always agreed on every issue, but (he) has shown a willingness to work in a bipartisan manner, put people over party, and do what is right for Pennsylvanians and all Americans."

Reid called Specter a "man of honor and integrity" who would be welcome in the Democratic caucus.

Specter was expected to face a very tough primary challenge next year from former Rep. Pat Toomey, who nearly defeated Specter in the Pennsylvania GOP Senate primary in 2004.

A Quinnipiac University survey of registered Pennsylvania voters released last month showed Specter trailing the more conservative Toomey in a hypothetical primary match-up, 41 to 27 percent.

A separate Franklin & Marshall survey showed Specter leading Toomey 33 to 18 percent. Another 42 percent, however, were undecided.

Over half of the Republicans polled in the Franklin & Marshall survey said they would prefer to see someone new in the Senate.

Numerous Republicans are very angry with Specter over his recent vote in support of Obama's $787 billion stimulus plan.

Specter, one of only three GOP senators to vote for the measure, has been part of a dwindling group of GOP moderates from the northeastern part of the country.