WASHINGTON - The family photographs came down Monday, packed in bubble wrap and boxes for the trip home, leaving nothing but some nails and sun-faded outlines on the walls of Pennsylvania Sen. Arlen Specter's inner office.

After 30 years on Capitol Hill, the state's longest-serving senator is clearing out and heading back to Philadelphia.

Specter, 80, will deliver his final floor speech Tuesday morning, decrying a gridlocked Senate that has lost its political center and the sense of collegiality that once kept senators from campaigning against one another.

"Eating or defeating your own is a form of sophisticated cannibalism," Specter, a Democrat, plans to say, according to his prepared remarks, referring to conservative Republican senators - notably Jim DeMint of South Carolina - who helped tea-party insurgents fell three moderate incumbents in the 2010 primaries.

"Collegiality can obviously not be maintained when negotiating with someone out to defeat you, especially in your own party," Specter says in the 2,600-word speech, scheduled for 10:30 a.m. "In some quarters, compromising has become a dirty word. . . . Politics is no longer the art of the possible when senators are intransigent in their positions."

In some ways, Specter's journey over the last 20 months sums up the plight of the homeless centrist: He was all but forced out of the Republican Party and was embraced by the White House and other top Democrats, but could not survive his new party's primary.

He says he is cheered by the triumph of Alaska Sen. Lisa Murkowski, a Republican who lost to a tea-party candidate in the primary but who has evidently won reelection as a write-in.

"Her victory proves that America still wants to be and can be governed by the center," Specter says in his remarks.

For three decades, Arlen Specter's life has been ruled by the rhythms of the Senate, its roll calls and recesses, its deals and debates. And he has been in public life in one form or another for twice as long.

Now, Specter has to figure out life outside the bubble. He plans to teach a course on the Supreme Court at the University of Pennsylvania School of Law and is weighing offers to join several law firms as senior counsel. He also wants to do commentary for NPR or a television network and hopes to be tapped for special assignments by President Obama's administration, much as former Sen. George Mitchell (D., Maine) has been.

Specter is leaving the Senate frustrated that he has not been able to get a vote on his longtime proposal to televise Supreme Court proceedings, and he includes a pitch for the idea in his speech - which he titles his "Closing Argument."

"He's going to hang in and keep working until midnight on his last day," said the senator's son, Philadelphia trial lawyer Shanin Specter.

"I've had so many friends and other people say after the loss that this will be a great chance for dad to relax," Shanin Specter said. "Not really. That's not in his personality. He doesn't put a value on relaxation. He loves to be focused, to work on problems, the harder the better."

Even in his final days in office, the senator was working on new legislation. Last week, Specter introduced a bill that would allow Holocaust survivors and the descendants of victims to sue in U.S. courts to recover the proceeds of Holocaust-era insurance policies.

In his valedictory, Specter asserts that the "abuse" of Senate rules has contributed to the dysfunction of the chamber, with filibusters increasing exponentially and secret "holds" by senators preventing confirmation of judges and government officials.

He argues that senators should be allowed to offer amendments to bills - a courtesy routinely blocked by recent majority leaders of both parties - and that those engaging in filibusters should have to talk on the floor instead of merely stating their intention to do so.

"By allowing senators to offer amendments and a requirement for debate, not just notice, I think filibusters could be effectively managed as they have in the past," Specter said. A simple majority vote of 51 senators, he said, should be enough to cut off filibusters on judicial and executive-branch nominees, instead of the current 60-vote requirement.

A contrarian moderate, Specter always made decisions according to his own calculus of pragmatism and idealism, confounding friend and foe alike.

He would alienate an important bloc of voters and teeter on the brink of extinction, then recover. To his political enemies, he was like the monster in a horror flick who springs to life in the final frame despite the hatchet sticking out of his back.

He was well into his campaign for a sixth term in April 2009 when he bolted the Republican Party to join the Democrats. Polls showed Specter could not have won the GOP nomination after casting the crucial vote for Obama's $825 billion economic stimulus.

Democrats rejected him in the primary earlier this year.

Specter, author of two books, is working on a third that will focus on his party-switching experience and the gridlock in Washington. He's been working with former aide Charles Robbins, who co-wrote the senator's first memoir, Passion for Truth, published in 2000.

The speech Specter will deliver Tuesday is devoid of soul-searching; he does not plan to discuss his mistakes or regrets, at least according to the text.

He has turned down numerous interview requests to discuss his future or his record. Asked to assess his career, he likes to reply that "it's too early."

Boxes of his papers and mementoes are designated to go into storage for the planned Specter library at Philadelphia University; others are heading to his longtime East Falls home.

Before his election to the Senate, Specter was a prosecutor, famous for corruption cases targeting Philadelphia magistrates and the Teamsters; Philadelphia district attorney; and a candidate for mayor and governor, and, briefly in 1996, for president. His name has appeared on ballots 26 times.

Perhaps most memorably, Specter is credited with developing the "single-bullet theory" as a young investigator with the Warren Commission investigating the 1963 assassination of President John F. Kennedy.

In the Senate, Specter has been known mostly for his influence on the federal judiciary; he participated in 14 confirmation hearings for Supreme Court justices and was the prime force as a moderate Republican in defeating the 1987 nomination of conservative Robert Bork and ensuring the 1991 confirmation of Justice Clarence Thomas by undermining the credibility of Anita Hill, who had accused the nominee of sexual harassment.

As a Republican, Specter was often an irritant to his party, especially on social issues such as abortion rights and stem-cell research. He voted with the GOP position 58 percent of the time over his career, according to Congressional Quarterly. That's a high degree of dissent by today's Senate standards.

He has been a much more reliable vote for Democrats since the switch.

Specter approached lawmaking with a "determined individualism," said G. Terry Madonna, the pollster at Franklin and Marshall College who specializes in state politics. "His centrism and intellect pushed him into the center of many controversies, enabling him to exercise considerable influence over the results."

Specter has been instrumental in increasing research spending at the National Institutes of Health from $12 billion a year to $30 billion since 1996, and he got an extra $10 billion for the NIH in the stimulus bill. Health has been more than a political issue to him - he has survived two bouts of Hodgkin's lymphoma, a brain tumor, and open-heart surgery.

Along the way, Specter also became an expert on the Middle East, with dozens of trips to the region and deep ties to the region's leaders, especially in Syria. He embraced a senator's traditional role of bringing federal money to his state. When Citizens Against Government Waste listed him in its "Pig Book" a few years ago, Specter said, "If they left me out, I'd be worried."

Specter's questioning of Hill during the 1991 Thomas hearings angered millions of women, and a female opponent nearly defeated him in his 1992 reelection campaign using that episode as her main argument.

By 2004, conservatives were furious with Specter for being insufficiently behind President George W. Bush's agenda, and he came within 17,000 votes of losing the GOP primary.

After that fall's election, Specter said Bush should not interpret his narrow reelection as giving him a mandate, and he cautioned the president against nominating Supreme Court justices who would vote to overturn the Roe v. Wade ruling that legalized abortion. The GOP caucus was in an uproar and almost denied Specter his long-cherished goal of chairing the Senate Judiciary Committee. He calmed the waters by pledging not to impose a litmus test on Bush nominees.

"Nine lives? I think I have 19," a relieved Specter said at the time.

This time, his political luck has run out.

The stimulus vote was anathema to the Republican base. Specter's approval rating fell 50 percentage points overnight among GOP voters, and he concluded he would not survive a primary challenge from former Rep. Pat Toomey, a conservative Republican.

Though he had powerful support, it was a bad election in which to be a 30-year incumbent, especially one who switched parties. Democratic Rep. Joe Sestak handily beat Specter in the May primary with a simple message: This guy is an opportunist, not one of us.

Specter is determined to make the most of his post-Senate career, to continue to have a voice in the big issues of the day.

The bare office walls, the bubble wrap and boxes, most likely mark only a transition to a new phase of his public life. And despite his trials of the last few years, Specter seems determined to close on a positive note.

"An extraordinary experience has come to an end," he says in his planned remarks on the Senate floor, but "I do not say 'farewell' to my continuing involvement in public policy, which I will pursue in a different venue. I leave with great optimism for the future of our country and the continuing vital role of the United States Senate in the governance of our democracy."

Contact staff writer Thomas Fitzgerald at 215-854-2718 or tfitzgerald@phillynews.com.