A retired State Department worker and his wife have been arrested on charges of spying for Cuba over three decades, using grocery carts among their array of tools to pass government secrets, according to an indictment unsealed Friday. The indictment says Walter Kendall Myers worked his way into higher and higher US security clearances while secretly partnering with his wife, Gwendolyn Steingraber Myers, as clandestine agents so valued by the Cuban government that they once had a private four-hour meeting with President Fidel Castro. David Kris, assistant attorney general for national security, described the couple's alleged spying for the communist government as "incredibly serious." The Myers' arrest come as the United States attempts to ease tensions with Cuba dating from the Cold War. Two months ago, the Obama administration acted to relax a trade embargo imposed on the island nation in 1962. A senior State Department official described the potential for damage as great and the timing unfortunate, noting that it could affect congressional support for the administration's recent attempts to engage Cuba. The official spoke on condition of anonymity because of the continuing investigation. Cuba is notorious for not paying its agents, said a former intelligence official speaking anonymously because of the highly sensitive matter. Indeed, court documents indicate the couple received little money for their efforts, but instead professed a deep love for Cuba, Castro and the country's system of government. The court papers describe the couple's spying methods changing with the times, beginning with old-fashioned tools of Cold War spying: Morse code messages over a short-wave radio and notes taken on water-soluble paper. By the time they retired from the work in 2007, they allegedly were sending encrypted e-mails from Internet cafes. The criminal complaint says changing technology also persuaded Gwendolyn Myers to abandon what she considered an easy way of passing information, by changing shopping carts in a grocery store. The document quoted her as saying she "wouldn't do it now. Now they have cameras, but they didn't then." Authorities say her comments came during a series of meetings with an undercover FBI agent posing as a Cuban spy in April. The Myerses fell for the ruse, authorities say, sharing with the agent their views of Obama administration officials who recently had taken over responsibility for Latin American policy and accepting a device to encrypt future e-mail. The couple, who live in Washington, was arrested Thursday and pleaded not guilty Friday in US District Court. They were ordered held in jail until a detention hearing scheduled for Wednesday. Their attorney, Thomas Green, would not comment. The two were charged with conspiracy to act as illegal agents of the Cuban government and to communicate classified information to the Cuban government. Each also is charged with acting as an illegal agent of the Cuban government and with wire fraud. Kendall Myers, 72, was known by the Cubans as Agent 202 and his 71-year-old wife went by both Agent 123 and Agent E-634, according to the indictment. The indictment says Kendall Myers disclosed to the State Department that he traveled to Cuba for two weeks in 1978, saying the trip was for personal and academic purposes. The next year, a Cuban government official visited the couple while they were living in the Western state of South Dakota and recruited them to be spies, the indictment says. At Cuba's direction, authorities say, Kendall Myers sought out jobs that would give him access to classified information. He applied for a position at the CIA in 1981. He did not get that but later was able to get work at the State Department, where his security clearances rose over the next two decades. Kendall Myers first worked as a lecturer at the Foreign Service Institute and later as a European analyst in the department's intelligence arm, the Bureau of Intelligence and Research, or INR, from 2000 until his retirement in October 2007. The position gave him access to extremely sensitive documents, analysis and policy papers from a variety of government agencies. The indictment says in his last year of employment, Kendall Myers viewed more than 200 intelligence reports related to Cuba. During his time at the intelligence bureau, officials there were dealing with the aftermath of the Sept. 11, 2001, terror attacks and the response as well as assessments in the run-up to the Iraq war. INR is known to have disagreed with Bush administration hawks over Saddam Hussein's weapons of mass destruction program, and Myers could have given the Cubans information about internal divisions over the decision to go to war. Court documents say among the information they passed was economic intelligence, which the former intelligence official said makes up much of what information Cuba is interested in from the United States. The official said the damage from the intelligence would extend beyond Cuba, because US investigators would assume that anything useful to Cuba's allies would have been passed to them by Havana. State Department spokesman Philip Crowley said the arrest culminated a three-year investigation of Myers, and Secretary of State Hillary Rodham Clinton has ordered a "comprehensive damage assessment" to determine what may have been compromised to the Cubans. The indictment seeks the return of all $1.7 million Kendall Myers earned in his State Department career, along with his $174,867 roll-over IRA account. Court documents say Castro came to visit the couple in a small house in Cuba where they were staying in 1995, after traveling through Mexico under false names. Kendall Myers reportedly boasted to the undercover FBI agent that they had received "lots of medals" from the Cuban government. They made other trips to Trinidad and Tobago, Jamaica, Mexico, Brazil, Ecuador and Argentina to meet with Cuban agents, the indictment says. Myers apparently sympathized with the Cuban ideology and revolution that put Castro into power. Court documents say he wrote in a personal journal in 1978: "I can see nothing of value that has been lost by the revolution. ... (T)he revolution has released enormous potential and liberated the Cuban spirit." He praised Castro as a "brilliant and charismatic leader" who is "one of the great political leaders of our time." And he called the United States "exploiters" who regularly murdered Cuban revolutionary leaders.