Representative Randy "Duke" Cunningham, an eight-term congressman and Vietnam war fighter pilot, pleaded guilty to bribery and tearfully resigned, admitting he took $2.4 million in bribes mostly from defence contractors in exchange for government business and other favours.
"The truth is I broke the law, concealed my conduct, and disgraced my office," the 63-year-old Republican said at a news conference on Monday.
"I know that I will forfeit my freedom, my reputation, my worldly possessions, most importantly, the trust of my friends and family."
He could get up to 10 years in prison at sentencing on 27 February on federal charges of conspiracy to commit bribery and fraud, and tax evasion.
Investigators said Cunningham, a member of a House Appropriations subcommittee that controls defence funds, secured contracts worth tens of millions of dollars for those who paid him off.
Cunningham was charged in a case that grew out of an investigation into the sale of his home to a defence contractor at an inflated price.
The congressman had already announced in July - after the investigation became public - that he would not seek re-election next year. But until he entered his plea, he had insisted he had done nothing wrong.
Cunningham's plea comes amid a series of Republican scandals: Representative Tom DeLay of Texas had to step down as majority leader after he was indicted in a campaign finance case; a stock sale by Senate Majority leader Bill Frist is being looked at by regulators; and Vice-President Dick Cheney's chief of staff was indicted in a case involving the leak of a CIA agent's identity.
In court documents, prosecutors said Cunningham, a former flying ace with the US Navy, admitted receiving at least $2.4 million in bribes paid in a variety of forms, including cheques totalling more than $1 million, cash, antiques, rugs, furniture, yacht club fees and vacations.
"The truth is I broke the law, concealed my conduct, and disgraced my office"
Among other things, prosecutors said, Cunningham was given $1.025 million to pay down the mortgage on his Rancho Santa Fe mansion.
"He did the worst thing an elected official can do - he enriched himself through his position and violated the trust of those who put him there," US Attorney Carol Lam said.
Cunningham was allowed to remain free while he awaits sentencing. He also agreed to forfeit his mansion, more than $1.8 million in cash, along with antiques and rugs.
Governor Arnold Schwarzenegger will have 14 days to set a date for an election to replace Cunningham, the governor's office said.
Cunningham is the first congressman to leave office amid bribery allegations since 2002, when former Representative James Traficant, an Ohio Democrat, was sentenced to eight years in prison after being convicted of racketeering and accepting bribes.
Schwarzenegger will call new
polls to replace Cunningham
The case began when authorities started investigating Cunningham's sale of his Del Mar house to defence contractor Mitchell Wade for $1,675,000.
Wade sold the house nearly a year later for $975,000 - a loss of $700,000 in a hot real estate market.
In addition to buying the home at an inflated price, Wade let Cunningham live rent-free on his yacht, the Duke Stir, at a yacht club.
Wade's company, MZM Incorporated, also donated generously to Cunningham's campaigns and was winning defence contracts around the same time.
The company does classified intelligence work for the military. It had $65.5 million of contracts for intelligence-related defence work in fiscal 2004, ranking No 38 on the Pentagon's list.
It has established a presence in Iraq, fielding a team of interpreters shortly after the US-led invasion.
Although prosecutors did not name Cunningham's four alleged co-conspirators, details in the plea documents, including business addresses and occupations, make clear that Wade was one of them.
The documents indicate another alleged conspirator was Brent Wilkes, an associate of Wade's who headed a defence contracting company called ADCS Incorporated that also provided campaign cash and favours to Cunningham while reaping valuable contracts.
The last alleged co-conspirator appears to be Thomas Kontogiannis, a New York developer.
Cunningham interceded with prosecutors on Kontogiannis' behalf when he had legal troubles, and a mortgage company run by Kontogiannis' relatives helped Cunningham finance an apartment in Virginia and his house in Rancho Santa Fe.
Attorneys for Wilkes and Wade declined to comment. Kontogiannis' attorney did not return a call.