Federal prosecutors will appear before a three-judge panel Wednesday to argue that former State Sen. Vincent J. Fumo, nearly midway through a 55-month sentence for corruption, should be resentenced to a longer term.

Once one of the most influential politicians in Philadelphia and Harrisburg, Fumo was convicted in 2009 on 137 counts of corruption and fraud. Prosecutors want a sentence that meets federal guidelines, which call for a much longer term of 21 to 27 years.

Legal teams will be limited to 20 minutes of oral argument each, according to the U.S. Court of Appeals for the Third Circuit.

Fumo was sentenced after the jury found that he had turned his Senate staff into personal servants and political minions, doing errands for him on state time. The jury also found that he had defrauded a pair of nonprofit organizations. After Fumo realized the FBI was on the trail, he tried to obstruct the probe.

The wrongdoings cost taxpayers and the nonprofit groups more than $2 million.

At sentencing, U.S. District Judge Ronald L. Buckwalter said the 55-month term was justified by Fumo's public service, 259 letters asking for leniency and extolling Fumo's work, and the nature of Fumo's offenses.

"It's not murder. It's not robbery. It's not even assault," Buckwalter said of Fumo's wrongdoings. "It's nothing violent. It's not the selling of a political office," Buckwalter said at Fumo's sentencing hearing.

His decision produced an outcry, and federal prosecutors are hoping the Third Circuit will send the case back for resentencing. Meanwhile, Fumo is asking for a new trial. The three-judge panel will decide both issues.

"It is likely impossible to identify a defendant in recent years who stole over $2 million, abused a position of public trust, and obstructed justice in the process who received a sentence anything like Fumo's," Assistant U.S. Attorney Robert Zauzmer wrote in the government's appeal.

Zauzmer declined to comment on the case in advance of the Third Circuit hearing. Fumo's defense team is also not discussing the hearing, said Dennis Cogan, one of three lawyers working on Fumo's case.

In their court filings, the defense attorneys argue that there were "no significant" errors in Buckwalter's sentencing and that the cost to taxpayers of Fumo's fraud was just below $2.5 million. A greater financial loss, as prosecutors insist occurred, would have likely meant a longer sentence.

Historically, persuading an appeals court to overturn a District Court sentence as too lenient has been difficult.

But two recent cases could affect the judges' decision.

In March, an appellate panel upheld a sentencing appeal by the U.S. Attorney's Office and ordered U.S. District Judge Timothy J. Savage to resentence two men who played supporting roles in a $40 million fraud case. The court found that Savage, who along with Buckwalter serves in the Eastern District of Pennsylvania, had made procedural errors by not fully explaining his decision to give one man probation and another a brief prison sentence, both sentences below the recommended federal guidelines.

In Fumo's case, prosecutors are also arguing that Buckwalter made a variety of procedural errors.

In a Chicago case, a panel of appellate judges overturned a sentence of house imprisonment for a former alderman and transferred the case to a different judge for resentencing.

In both cases, the prosecutors' arguments were similar to those being made by prosecutors in Fumo's case: that the judges erred in calculating the financial loss caused by the crime and did not follow the complex rules governing sentencing.

Contact staff writer Nathan Gorenstein at 215-854-2797 or ngorenstein@phillynews.com.