BY LESLEY CLARK

Former State Department employee Walter Kendall Myers and his wife, Gwendolyn Myers, accused last week of being Cuban spies, will be held in custody until their trial because prosecutors consider the couple ''a serious flight risk,'' a U.S. magistrate in Washington decided Wednesday.

The magistrate sided with federal prosecutors who argued during the detention hearing that the Myerses are accomplished sailors who own a ''seaworthy'' vessel. Prosecutors said that if the couple fled to Cuba, the court -- and the U.S. government -- would have no authority to get them back.

Assistant U.S. Attorney Gordon Michael Harvey also noted that the Myerses could seek refuge in the Cuban Interests Section in Washington, D.C., which he said was less than three miles from their apartment.

Harvey said the couple has the means to leave as well, noting that Walter Kendall Myers has an inheritance and $500,000 in investments.

The couple attended the hearing in blue jail uniforms, listening intently as Harvey said they could pose a ''real and present danger . . . to the United States.'' He added that Fidel Castro had expressed praise for them in a weekend column and that the Myerses ''would be greeted as heroes -- they would not be coming back'' if they made it to Cuba.

An attorney representing the Myerses, Tom Green, asked that they be allowed to stay home under law enforcement supervision with ankle bracelets. He said the sailboat could be "disabled.''

''Conditions could be fashioned'' to allow them out of jail, he said, noting that Walter Kendall Myers is a "lifelong resident of the District of Columbia.''

The couple has been held without bond since pleading not guilty Friday to charges of conspiracy, wire fraud and acting as illegal agents for the government in Havana.

Prosecutors allege Cuba recruited Myers after a 1978 trip to the island and that, over the years, Myers and his wife traveled to Mexico, the Caribbean, South America and New York, meeting with Cuban agents to divulge U.S. secrets.

They say the couple kept in touch with their Cuban handlers via a shortwave radio -- the same make as the one owned by convicted Cuban spy Ana Belen Montes. In court documents, Myers is quoted as saying he was so successful he received ''lots of medals'' from the Cuban government and that he and his wife enjoyed a rare private meeting in 1995 with Fidel Castro.

Their trips out of the United States tapered off after 2005, when Myers began to get ''paranoid'' that he was on a watch list. He retired from the State Department in 2007, but U.S. prosecutors say the Cuban Intelligence Service kept in touch via e-mail, asking to meet the couple in Mexico.

The State Department is conducting a review to determine what Myers may have divulged to the Cubans, and Secretary of State Hillary Rodham Clinton said she has ordered a security review to prevent a repeat of what she called an ''outrageous violation'' of Myers' oath to serve.

The arrests come as President Barack Obama has sought to improve relations with Havana and observers suggest it could hamper the resumption of planned migration talks between the two countries.

On Wednesday, Harvey called the government case ''very strong'' -- but Green noted more serious charges of espionage haven't been filed, calling the government's case "somewhat embellished.''

The magistrate asked the federal lawyers whether the government would be adding espionage to the charges.

Harvey said the investigation is continuing. He said investigators have access to computer files, "and that we may well be looking at additional charges against the Myerses.''

During the hearing, Walter Kendall Myers, wearing glasses, stroked his mustache with an index finger. He sat with his hands folded across his chest for most of the argument. His wife sat next to him, fingers laced in front of her on the table, sitting up straight.

Green said the Myerses have four children between them. Gwendolyn Myers' son, Brad, was in the front row for the hearing.

Miami Herald staff writer Carol Rosenberg contributed to this report.