WASHINGTON - 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 yesterday.

U.S. Magistrate Judge John Facciola sided with federal prosecutors who argued during the detention hearing that the Myerses were 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 Michael Harvey also noted that the Myerses could seek refuge in the Cuban Interests Section in Washington, which he said was less than three miles from their apartment.

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

The couple attended the hearing in blue jail uniforms, listening 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, adding that Walter Kendall Myers was a "lifelong resident of the District of Columbia."

Green noted more serious charges of espionage had not 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 was continuing and there could be other charges.

The couple have 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 that 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.

They say the couple - he is 72, she is 71 - kept in touch with their Cuban handlers via a shortwave radio.

In court documents, Myers is quoted as saying that 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 Castro.