LONDON — One of the Cold War's most famous defectors said Tuesday that Russia may have as many as 50 deep-cover couples spying inside the United States.

Oleg Gordievsky, a former deputy head of the KGB in London who defected in 1985, said President Dmitry Medvedev would know the number of illegal operatives in each target country.

The 71-year-old ex-double agent said that, based on his experience in Russian intelligence, he estimates that Moscow likely has 40 to 50 couples operating undercover in the United States.

"For the KGB, there's usually 40 to 50 couples, all illegal," said Gordievsky, who defected to Britain after supplying information during the Cold War to Britain's MI6 overseas spy agency.

Gordievsky said he spent nine years working in the KGB directorate in charge of illegal spy teams.

"The president will know the number, and in each country how many — but not their names," Gordievsky said.

The FBI announced Monday the arrests of 10 alleged deep-cover Russian agents after tracking the suspects for years. They are accused of attempting to infiltrate U.S. policymaking circles while posing as ordinary citizens.

Gordievsky said he estimates that there are 400 declared Russian intelligence officers in the United States, and likely 40 to 50 couples charged with covertly cultivating military and diplomat officials as sources of information.

He said the complexity involved in training and running undercover teams means that Russia is unlikely to have significantly more operatives than during his career.

"I understand the resources they have, and how many people they can train and send to other countries," Gordievsky said. "It is possible there may be more now, but not many more, and no more than 60."

He said deep-cover spies often fail to deliver better intelligence than their colleagues who work in the open.

"They are supposed to be the vanguard of Russian intelligence," Gordievsky said. "But what they are really doing is nothing, they just sit at home in Britain, France and the U.S."

He said that undercover operatives may report to Russia once or twice a year, but otherwise work largely without any support network.

"The illegals don't have the support of the office behind them, and they are very timid as a result, so they don't produce a lot," Gordievsky said.