PHILADELPHIA — US Representative Chaka Fattah took an illegal $1 million loan to prop up an ailing mayoral bid and obtained federal funds and charity grants to pay most of it back, federal prosecutors said Monday as they outlined their racketeering case on the opening day of his trial.

Fattah, a Philadelphia Democrat, went on trial just weeks after losing a primary race to retain the congressional seat he had held for two decades.

The loss comes in a year that has seen his son go to prison for five years in a related fraud case and his wife lose her TV anchor job after being linked to a bribery count in the indictment.

Renee Chenault-Fattah has not been charged, and both husband and wife insist they did nothing illegal. Chaka Fattah, 59, blames his family’s travails on an FBI investigation that he calls a witch hunt. Federal prosecutors painted a starkly different picture.

‘‘The congressman stole from federal agencies, from taxpayers, from nonprofit groups he created to pay his political debts,’’ Assistant US Attorney Paul Gray said in opening statements. ‘‘He even stole from his own campaign.’’

Four associates are also on trial, while two others pleaded guilty and are expected to cooperate. Fattah’s lawyers told jurors that campaign consultants Greg Naylor and Thomas Lindenfeld acted alone.

The campaign loan, which exceeded donor limits for the 2007 mayor’s race, is one of five schemes outlined in the racketeering indictment.

The others include the use of nonprofits Fattah set up as ‘‘pass throughs’’ for federal grants to reach his family and friends, prosecutors said.

Associated Press