A husband and wife from Miami accused of being members of a spy ring for Cuba became Wednesday the first of 10 suspects to plead guilty in the case.

Appearing before U.S. District Judge Joan Lenard, Nilo and Linda Hernandez admitted that they served Havana as unregistered foreign agents.

Assistant U.S. Attorney Caroline Heck Miller told the court that Nilo Hernandez, 44, counted aircraft at Homestead Air Force Base. She said he had a shortwave radio in his house.

According to an FBI affidavit, both were directed to infiltrate anti-Castro groups. For example, Linda Hernandez, 41, monitored the activities of Miami-based Alpha 66.

Computer records seized by agents, according to court papers, referred to them as sub-agents or ''Juniors'' who held the military rank of ''sublieutenant.''

They were asked by their government to ''conduct an investigation'' of an unnamed local telecommunications company, and directed to develop closer relations with a former U.S. Navy employee ''to determine his reaction to assisting them by providing information.''

Federal prosecutors and agents have said that the ring used shortwave radios to communicate back home to Cuba, and stored vast amounts of coded information on computer disks.

Defense attorney Richard Diaz, who represents the husband, told The Herald that the Cuban government didn't pay the couple directly, but forwarded money to their relatives in Cuba.

''They tried to get out of the ring and that's when pressures were out on them to continue when certain benefits and payments were withdrawn from the families,'' Diaz said.

Diaz and co-counsel Vincent Farina have insisted since the case began that the Hernandezes were not guilty of espionage, but of a technical violation of laws that govern foreign agents.

''They basically confessed to what they were charged with after their arrests,'' Diaz said.

''The plea agreement gives them the option to cooperate. That is something we would have to look into with the government,'' Diaz said. ''I have not encouraged or discouraged them from cooperating. I've warned them about the positives and negatives about it.''

The maximum penalty is 10 years in prison and a fine of $250,000. Diaz predicted federal sentencing guidelines would place the prison term in the two- to three-year range. Lenard scheduled a Feb. 3 sentencing for Nilo Hernandez and set his wife's sentencing for the next day.

A grand jury handed up an indictment against all 10 defendants last Friday -- several weeks after the FBI rounded them up at various locations in Broward, Miami-Dade and Monroe counties. Authorities said the sweep of suspected spies for Cuba was the biggest in memory.

Three men are accused of conspiring to commit espionage -- a charge that carries a life sentence. Most of the others are accused of failing to register as foreign agents with the U.S. attorney general.

More pleas may be forthcoming amid predictions by defense attorneys that a trial might not occur for 18 months.

Because the case centers on espionage and spying, attorneys require security clearances, and the court must establish a process for them to review classified documents under the Classified Information Procedures Act.