PHILADELPHIA — Federal prosecutors stung by this week's 55-month sentence for a long-powerful Pennsylvania lawmaker in a sprawling corruption case will seek to appeal the ruling.

Prosecutors call Vincent Fumo's term "unduly lenient and unreasonable" and plan to ask the Justice Department to sign off on an appeal.

Fumo, a Philadelphia Democrat who amassed vast power during 30 years in the state senate, was sentenced Tuesday for misappropriating millions from the coffers of the state senate and two nonprofits.

"In opinion articles, letters to the editor, e-mails, blog postings, and a flood of phone calls to our office and, we believe, to this Court, thousands of citizens expressed their dismay at the unduly lenient sentence imposed on Fumo," prosecutors wrote in court papers filed Friday.

U.S. District Judge Ronald Buckwalter sentenced Fumo well below the 20-plus years recommended by probation or his own guideline calculation of more than 10 years. Buckwalter credited Fumo's public service and mostly dismissed government claims that his crimes eroded public trust in the political system.

By week's end, even Gov. Ed Rendell — who had written a character letter on Fumo's behalf — suggested an appeal was appropriate.

Fumo, 66, is due to report to prison on Aug. 31. He must also pay $2.4 million in restitution and fines. Prosecutors argued that he defrauded the senate and charities of more than $4 million.

They disclosed their plans to appeal in a sentencing memo filed Friday for co-defendant Ruth Arnao, who faces sentencing Tuesday on 45 counts.

Arnao was a top aide and trusted friend to Fumo. She is married to former state turnpike commissioner Mitchell Rubin, the target of an FBI investigation into $150,000 in alleged "no-work" senate contracts Fumo awarded him.