(CNN) -- Rep. Randy "Duke" Cunningham said Monday he is resigning from Congress after pleading guilty to taking more than $2 million in bribes in a criminal conspiracy involving at least three defense contractors.After entering his plea in San Diego, California, the eight-term California Republican said he was "deeply sorry.""The truth is I broke the law, concealed my conduct and disgraced my office," he told reporters, his voice strained with emotion. "I know I will forfeit my reputation, my worldly possessions -- most importantly the trust of my friends and family." (Watch: 'Now I know great shame' -- 2:16)Asked by U.S. District Judge Larry Burns if he had accepted cash and gifts and then tried to influence the Defense Department on behalf of the donors, Cunningham said, "Yes, your honor."Cunningham's plea agreement with federal prosecutors stemmed from an investigation of the 2003 sale of his California home to a defense contractor for an inflated price.Under the agreement, Cunningham acknowledged a conspiracy to commit bribery, mail and wire fraud and tax evasion. He also pleaded guilty to a separate tax evasion violation for failing to disclose income in 2004.Prosecutors said Cunningham had taken bribes from contractors, which enabled him to buy a mansion, a suburban Washington condominium, a yacht and a Rolls Royce.A government statement said Cunningham received at least $2.4 million in bribes and will forfeit his $2.5 million mansion and about $1.8 million in cash, antiques, furnishings and other valuables.The charges carry a potential penalty of 10 years in prison and up to $350,000 in fines. Sentencing is scheduled for February 27."The citizens who elected Cunningham assumed that he would do his best for them," said U.S. Attorney Carol Lam. "Instead, 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."Cunningham, 63, sold his San Diego-area house in 2003 for $1.6 million to defense contractor Mitchell Wade, who then sold it for $700,000 less. The transactions sparked allegations that the contractor had bought the house at the higher price as payback for Cunningham's pressing the Pentagon to award contracts to the defense contractor.Cunningham, whose annual salary is about $160,000, then bought the $2.5 million mansion.Over the summer, federal agents raided Cunningham's California home, a boat he lives on while in Washington and the Washington offices of Wade's former employer, defense contractor MZM Inc.A decorated former Navy fighter pilot who shot down five MIGs in Vietnam, Cunningham served as an instructor in the Navy's famed "Top Gun" program."I learned in Vietnam that the true measure of a man is how he responds to adversity," he said. "I can't undo what I have done, but I can atone.""I'm almost 65 years old and I enter the twilight of my life. I intend to use the remaining time that God grants me to make amends, and I will."Cunningham would not respond to questions. "This is now a personal matter for the congressman and his family," said Harmony Allen, his chief of staff, in a written statement. "The office will not comment any further on today's proceedings other than to say that we are praying for Duke in these exceedingly difficult times." Cunningham was first elected in 1990. He represented the 50th District, which includes parts of San Diego and its northern suburbs. The district is solidly Republican.He served on a powerful defense appropriations subcommittee that approves spending for defense programs.Cunningham said in July that he wouldn't seek a ninth term next year; denying any wrongdoing at the time, he said that he intended to finish the remainder of his current term.The congressman said then that he decided not to run for re-election in part because of the toll the investigation had taken on his family and standing in the community. (Full story)"I publicly declared my innocence because I was not strong enough to face the truth," he said Monday. "So I misled my family, friends, staff, colleagues, the public, and even myself."In a written statement, House Minority Leader Nancy Pelosi, a California Democrat, said the case "is just the latest example of the culture of corruption that pervades the Republican-controlled Congress, which ignores the needs of the American people to serve wealthy special interests and their cronies."Special electionCunningham's resignation will trigger a special election for his Southern California House seat, and at least half a dozen candidates are expected to make bids to succeed him.Some had begun taking steps to run for the seat after Cunningham announced in July that he would not seek re-election.Under California law, all candidates will appear on the same ballot in a special primary election to be held in January. If no single candidate receives more than half of the votes, a general election of the top vote-getters representing each political party would be held in March.The governor must specify within 14 days a date for the election.Despite Cunningham's admission of guilt, Democrats could have a hard time winning his seat. Last year, Cunningham easily defeated his Democratic opponent, Francine Busby, 58 percent to 36 percent.And President Bush beat his Democratic opponent, Sen. John Kerry of Massachusetts, 55 percent to 44 percent in the district."It is a Republican seat," said Carl Forti, a spokesman for the National Republican Congressional Committee. "Even before the resignation, Democrats didn't have anybody running, and I wouldn't expect that to change."Busby is running again, and several Republicans have already announced or are eyeing a run, including ex-U.S. Rep. Brian Bilbray, ex-state assemblyman Howard Kaloogian, state Sen. Bill Morrow, businessman George Schwartzman and businessman Alan Uke.CNN's Ed Henry and Mark Preston contributed to this story.