WASHINGTON -- A retired State Department worker and his wife accused of three decades of spying for Cuba are preparing to plead guilty in the case, according to a Friday court filing.

Walter Kendall Myers, 72, and wife, Gwendolyn, 71, were caught in an undercover FBI sting operation, arrested in June and held without bail.

According to a so-called criminal information filed by the Justice Department in federal court, Walter Myers is prepared to admit to plotting to commit espionage and wire fraud. Such a legal document is filed with the consent of the defendant and is the first step toward entering a guilty plea.

The document indicates Walter Kendall will admit that he was known as "Agent 202," and that he and Gwendolyn began a conspiracy in 1979 to provide national security information to the government of Cuba. The couple married three years later.

A second document shows his wife, also known as "Agent 123," plans to plead guilty to a single count on a lesser charge of conspiring to gather and transmit national defense information.

The filings do not indicate when a plea hearing might be held or what sort of prison sentence each is likely to receive. However, since the wife is pleading to fewer charges, it is likely she will face a shorter sentence.

U.S. authorities say the Myerses delivered government secrets to Cuban agents over the past 30 years using a shortwave radio, by swapping carts at a grocery store and in at least one face-to-face meeting with former Cuban leader Fidel Castro in Cuba.

Key evidence in the case came from an undercover operation involving an FBI agent who approached Kendall Myers on the street on the defendant's birthday, April 15. The agent gave Kendall Myers a cigar, said he knew his Cuban handler and asked that they meet later.

The ruse worked, and the Myerses met three times with the agent at Washington hotels over the next two weeks. The FBI secretly videotaped the sessions, in which they say the couple made many incriminating statements about their time as spies.

In one of those sessions, Gwendolyn Myers allegedly proposed to the undercover FBI agent that her husband could be an instructor at a Cuban intelligence academy.

"So when can we come?" she allegedly said.