* State prosecutor to present final views on Thursday
* Erdogan stresses battle against anti-democratic forces
* Opposition accuses government of silencing opposition
By Daren Butler
ISTANBUL, Dec 11 (Reuters) - Prime Minister Tayyip Erdogan's decade-old battle with secularist opponents in Turkey is approaching a decisive moment as nearly 300 people charged with attempting the violent overthrow of his government prepare their final defences.
In a courthouse within a huge prison complex near Istanbul, a state prosecutor will sum up his case this week against the defendants accused of membership of "Ergenekon", an alleged underground network of nationalist coup plotters.
The trial has drawn accusations of political influence over the judiciary. The defendants are a diverse crowd including politicians, academics, journalists and retired army officers, notably former armed forces chief Ilker Basbug.
Ergenekon is accused of being at the heart of political violence, extra-judicial killings and bomb attacks which scarred Turkey in recent decades - an embodiment of anti-democratic forces which Erdogan says he has fought to stamp out.
His critics see a ploy to stifle opposition, part of a grand plan by the leader to tame the secularist establishment, including an army that intervened to topple governments four times in the second half of the 20th Century.
The main opposition party CHP, two of whose deputies are among the 275 defendants, has called on its members to gather at the courthouse on Thursday to protest at what it has dubbed an "inquisition" of government critics.
"You've thrown journalists in jail, you've thrown scientists in jail, you've thrown everyone in jail. You've created concentration camps in 21st Century Turkey," CHP leader Kemal Kilicdaroglu told parliament on Monday, citing a doubling in the jail population to 125,000 from 59,000 in 2002.
Erdogan responds by accusing his secularist opponents of siding with anti-democratic forces and fuelling fears that his Islamist-rooted AK Party was seeking to undermine by stealth the secular foundations of the Turkish Republic.
"Those who present our successes as a settling of accounts with the Republic should first come out and question their role in interventions, their stances in support of coups," he said.
"For decades Turkey has lost energy with artificial disputes, imaginary fears, with a mentality creating paranoia saying...'the Republic is in danger', 'secularism is slipping away', 'religious fundamentalism is coming'."
After four years of legal process, the prosecutor is due to present his final opinion on the case on Thursday or Friday. There will then be a final right of defence for those in the dock which, given the number of defendants involved, could still take months.
The alleged Ergenekon network is named after a legend in which a wolf - still the symbol of Turkish ultranationalists - leads the Turks through mountain passes out of a Central Asian valley where they had been trapped for centuries, allowing them to found Turkic states.
Investigation of the alleged conspiracy, which surfaced in 2007 when police discovered a cache of weapons in Istanbul, was initially welcomed by a public eager to see an end to the "Deep State" - a shadowy network of militant secularists long believed to have been pulling the strings of power.
Erdogan highlighted government efforts to crack down on such forces in a response last month to a parliamentary commission investigating Turkey's history of military coups.
"For 10 years the AK Party government has fought ... to clean up gangs and dark forces," he wrote. " Many games targeting our government and the national will have been spoiled, many illegal initiatives have been taken up by the judiciary."
But dissenting voices have grown over the last five years, with the European Commission expressing concern about the handling of the conspiracy trials in its latest progress report on Turkey, a candidate for EU membership.
"Concerns persisted over the rights of the defence, lengthy pre-trial detention and excessively long and catch-all indictments," the report said, saying the cases contributed to the polarisation of Turkish politics.
One of the main worries abroad is the number of journalists held in jail, although most of these are accused of links to Kurdish militants rather than Ergenekon. A Committee to Protect Journalists report on Tuesday described Turkey as "the world's worst jailer with 49 journalists behind bars".
Defence lawyer Celal Ulgen said the trial is designed "to silence Turkey's intellectuals, to re-design the Turkish Armed Forces, to ensure the government controls the ways in which it can be opposed".
Among the most prominent suspects are former armed forces chief General Basbug, who has angrily dismissed accusations that he is a leader of a "terrorist organisation" as a "comedy".
Erdogan has denied interfering in the legal process. In his response to the coup commission, he praised the judiciary.
"Our prosecutors and judges have courageously done their duty," he wrote. "What our government has done in this process is to make possible the smooth functioning of the judiciary and to watch patiently as justice takes shape." (Additional reporting by Ece Toksabay; Writing by Daren Butler; Editing by Nick Tattersall and Tom Pfeiffer)