* Guerrilla's leave triggers Greek outcry
* November 17 targets included U.S., British diplomats
* U.S., British ambassadors express regret (Adds U.S., British ambassador comments)
ATHENS, Nov 9 (Reuters) - A leading member of Greece's most deadly guerrilla group, November 17, began a two-day leave from prison on Thursday under a parole board ruling that triggered a storm of protest and expressions of regret from Britain and the United States.
Dimitris Koufodinas is serving several life terms for his role in the Marxist group that operated for almost three decades until Greek authorities arrested its leaders in 2002.
Its targets ranged from businessmen to diplomats. Its first victim was a CIA station chief in 1975, and its last a British embassy defence attache in 2000.
Prison authorities granted his request for temporary leave from jail on condition he report to a police station twice a day. It is his first such leave since he was jailed in 2003 and authorities said it was in compliance with regulations applying to all inmates.
But the release comes at a sensitive time for the government, which is frequently accused by opposition parties of being soft on anti-establishment groups with roots in leftist radicalism and anarchy.
Conservative lawmaker Dora Bakoyannis, whose husband Pavlos Bakoyannis was gunned down by November 17 in 1989, was visibly angry during a live broadcast after his release from jail.
"He isn't just any terrorist. He was a leader, the ideological guide, the guy who wrote a book who said that after the murder (of Bakoyannis) he went to a tavern and celebrated. While my children were crying," she told Skai TV.
Geoffrey Pyatt, the U.S. ambassador to Greece, said in a Tweet the decision was a "dishonour" to the memory of victims and their families.
British ambassador Smith said she was "deeply disappointed" and shared the victims' pain.
Both envoys carried photos of plaques at their respective embassies commemorating November 17 victims.
Members of November 17 eluded capture for years. The country has a history of political violence and still has urban guerrilla groups, though none as deadly as November 17.
Koufodinas, an amateur beekeeper known as 'poison hand' for the precision of his aim, has been kept at a high-security jail in Athens for 15 years. There, he wrote two books, one called "I was Born November 17", and the second "13 Answers".
In a high profile trial in 2003, 15 people, including Koufodinas, were found guilty over the 23 killings and dozens of bomb attacks claimed by the guerrilla group.
A government official said authorities followed procedure. "I am not going to defend the practice, the deeds, nor the ideology of Mr Koufodinas," he told Real FM radio. "What I can say as a comment is that in this specific case the law was applied to the letter, and the preconditions were met for granting leave."
The group took its name from the date of a 1973 student uprising against the military dictatorship. It is normally marked every Nov. 17 with street protests in Athens. (Reporting By Michele Kambas; Editing by Matthew Mpoke Bigg)
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