Sagging in the polls as well as his fund-raising, mayoral candidate Chaka Fattah has turned to someone who seems to share none of those same problems: U.S. Sen. Barack Obama.

An e-mail yesterday sent to Fattah supporters contained a plea from Obama to send money - "$500, $100, $50 or $25 right away, so Chaka can get his message to voters in this crucial week before the May 15th election."

Fattah, a seven-term congressman, began the mayoral primary race as the Democratic front-runner. Recent polls show him third, behind Tom Knox and Michael Nutter. He also raised less money in the first four months of this year than any of his four main Democratic rivals.

Enter Obama.

"In 25 years of public service on the local and national levels, Chaka has never forgotten his early life lesson: The key to breaking the grip of violence in our most hard-pressed communities is to replace desperation with hope," the Illinois senator who wants to be president wrote.

"To win this election, Chaka doesn't need to match the other candidates dollar for dollar, but he does need a strong push this week," he wrote.

Obama then went on to compare his own 2004 Senate race, in which he faced a wealthy opponent buying masses of TV time, to Fattah's challenge to turn back not just Nutter but Knox, a millionaire health executive who has poured $8 million of his own into his campaign.

"By organizing a first-rate field operation and getting our supporters to the polls, we turned that conventional wisdom on its head," the e-mail read. "With your help Chaka can do the same thing."

Fattah yesterday was pleased to get the help.

"That was strong, wasn't it?" a smiling Fattah said yesterday as he was leaving a campaign stop at the Reading Terminal Market.

This is not the first time Fattah has turned to Washington for help. In the fall, he held a Philadelphia fund-raiser for his congressional race that featured Bill Clinton as headliner.

And for months on the campaign trail, Fattah has been given to quoting Obama and comparing their life stories.

"Obama says it, and it's true for me, that my experiences are the foundation for everything I do," Fattah told a reporter last month, referring to the senator's memoir The Audacity of Hope.

Two of Fattah's key campaign strategists, Tom Lindenfeld and Greg Naylor, also played central advisory roles in helping Obama win his Senate seat - a point Fattah likes to make time and again.

Contact staff writer Marcia Gelbart at 215-854-2338 or mgelbart@phillynews.com.

Staff writer Patrick Kerkstra contributed to this story.