HOUSTON -- A federal judge threw out the conviction of a former CIA operative who has spent 20 years in prison for selling arms to Libya, saying the government knowingly used false evidence against him.

Edwin P. Wilson, 75, was convicted in 1983 of shipping 20 tons of C-4 plastic explosives to Libya -- something he said he did to ingratiate himself with the Libyan government at the CIA's request.

U.S. Judge Lynn N. Hughes said the federal government failed to correct information about Wilson's service to the CIA that it admitted internally was false.

The ruling's immediate effect was not clear because Wilson received prison time for two other convictions -- including one for conspiring to have prosecutors killed.

The CIA declined to comment specifically on the ruling.

"The CIA didn't authorize or play any role whatsoever in his decision to sell arms to Libya," agency spokesman Mark Mansfield said. "That decision was his and that is why he went to jail."

The Justice Department will review the decision and study its options, a spokesman said.

"Beyond that, there's not much that we would comment on at this point," Bryan Sierra said.

At his 1983 trial in Texas, prosecutors introduced a sworn statement from a top-ranking official that Wilson didn't do anything for the CIA after his retirement in 1971.

"It was just a flat-out lie. He did a lot," Adler said Tuesday.

Adler said the Reagan-era officials who pushed the case had been embarrassed by revelations they were trading arms for information and made Wilson a scapegoat.

"For over 20 years he's been claiming he was not some kind of rogue CIA officer and he did not get a fair trial and, of course, it turns out he was right," Adler said.

Days after his conviction, but before his sentencing, the CIA forwarded a memo to the U.S. attorney's office saying at least five projects Wilson had worked on for the CIA after 1971 had surfaced -- including a planned trip to Iran with the CIA's deputy director.

Hughes said officials failed to inform Wilson's attorneys of the memo and that in his appeal, the government failed to acknowledge that the affidavit was false and suppressed other evidence that might have helped him.

The memo and documents about later discussions were obtained by Wilson's defense under the Freedom of Information Act and through court discovery for his 1999 appeal.

Prosecutors have the option of appealing the judge's ruling or retrying Wilson. Adler said he didn't expect prosecutors to appeal, but U.S. Attorney Michael Shelby of the Southern District of Texas said his office had not made a decision.

"Obviously the charges are very significant and we want to make sure we do the right thing," Shelby said in a story in Wednesday's Houston Chronicle.

Wilson, who set up front companies abroad for the CIA and posed as a rich American businessman, is serving a 52-year prison sentence in a federal prison in Allenwood, Pa.

In 1982, he was lured out of hiding in Libya and brought to New York for arrest. A federal court in Virginia convicted him of exporting firearms to Libya without permission and sentenced him to 10 years.

He was convicted in Texas in 1983, receiving a 17-year sentence for similar crimes, and a New York court sentenced him to 25 years, to run consecutively with the Texas and Virginia sentences, for attempted murder, criminal solicitation and other charges involving claims that Wilson conspired behind bars to have witnesses and prosecutors killed.

With the Texas sentence thrown out, Wilson could be eligible for parole this year or next year based on time already served in the other cases, Adler said. Wilson also could seek to have the Virginia case overturned, he said. If successful in that effort, he would probably be eligible for immediate release, he said.