Kevin James, 31, and Levar Haley Washington, 28, entered their pleas in separate appearances before U.S. District Court Judge Cormac J. Carney. Washington also pleaded guilty to using a firearm to further the conspiracy. Prosecutors said he used a shotgun to rob a Torrance gas station on July 4, 2005.
James faces up to 20 years in prison when he is sentenced March 31. Washington faces up to 20 years in prison on the conspiracy charge and five years to life for the firearms offense when he is sentenced April 28.
Authorities say James, Washington and two others were part of a California prison gang cell of radical Muslims that planned the attacks in the Los Angeles area.
"Homegrown terrorism remains a grave concern to the security of our country, and this cell was closer to going operational at the time than anyone since 9/11," Los Angeles Deputy Police Chief Michael Downing told reporters at a news conference after the two men entered their pleas.
Police uncovered the plot in July 2005 while investigating a string of gas station robberies that authorities say were committed to finance the attacks. Torrance Police Chief John Neu told reporters at the news conference that authorities linked about 10 holdups to the plot.
The plotters were within weeks of being able to carry out an attack, officials said, when they were discovered about two months before the Jewish holiday Yom Kippur.
Washington and James, who arrived in court in chains and prison jumpsuits, said little during their separate hearings, answering Carney's questions with monosyllabic responses. Both men wore goatees and Washington's face was covered in tattoos.
Washington's attorney, Ellen Barry, said outside court that her client decided it was "in his best interests" to plead guilty. James' attorney, Robert Carlin, declined to comment.
Assistant U.S. Attorney Greg Staples said as a result of the plea agreement James' maximum possible sentence was reduced from 25 years to 20. U.S attorney spokesman Thom Mrozek said prosecutors would recommend an 18-year sentence for James and 25 years for Washington.
Also indicted in the case were Gregory Vernon Patterson and Hammad Riaz Samana. All but Samana, a Pakistani national, are American-born Muslim converts.
Patterson and Samana are charged with conspiracy to levy war against the U.S. government through terrorism, conspiracy to possess and discharge firearms in a violent crime, conspiracy to kill members of the U.S. government uniformed services and conspiracy to kill foreign officials. Patterson is also charged with a robbery count and using a firearm in a violent crime.
U.S. Attorney Thomas O'Brien said Samana has been declared mentally unfit to stand trial and is undergoing psychiatric care at a federal prison facility. Patterson is expected to plead guilty to a terrorism conspiracy charge on Monday.
Prosecutors say the plot was orchestrated by Washington, Patterson and Samana at the behest of James, a California State Prison, Sacramento, inmate who founded the radical group Jamiyyat Ul-Islam Is-Saheeh, or JIS.
Washington converted to Islam while imprisoned with James, then looked to recruit other members of the group, authorities said. Neu said Patterson and Samana were recruited in part because they had no criminal records and could acquire weapons without suspicion.
James preached that JIS members should target for violent attack any enemies of Islam or "infidels," including the U.S. government and any supporters of Israel, according to court documents.
He also created a document he called the "JIS Protocol," which advocated the establishment of an Islamic caliphate in the U.S. that followed Shariah law, or Islamic law.
"Sit back, build and attack!" prosecutors say James wrote in his document. "Our obvious targets being the Western forces of the U.S. and their ... society."
James spelled out in a separate document that JIS members must learn Arabic, acquire two pistols with silencers, learn bomb-making and become "legitimate."
"Acquire identification, drivers license ... keep regular contact with your parole agent," prosecutors say James wrote. "Your dress code must not bring attention. ... We have work to do."
Prosecutors assert that James also prepared a press release that the men planned to send out after an attack.
"This incident is the first in a series of incidents to come in a plight to defend and propagate traditional Islam in its purity," James allegedly wrote. "We are not extremists, radicals, or terrorists. We are only servants of Allah."