* Court verdict illustrates civilian dominance over military
* Defence, opposition allege political interference in case
* Lawyer says will appeal to European rights court
By Gulsen Solaker
ANKARA, Oct 9 (Reuters) - Turkey's appeals court upheld convictions on Wednesday of top retired military officers for leading a plot to overthrow Prime Minister Tayyip Erdogan's government a decade ago, in a case underlining civilian dominance over a once all-powerful army.
Relatives of the retired officers wept after the ruling and a defence lawyer said he would take the case to Europe's top human rights court.
The judges overturned convictions of dozens of less prominent defendants among more than 300 officers sentenced in September 2012 over the "Sledgehammer" conspiracy, said to have included plans to bomb Istanbul mosques and trigger an army takeover.
Turkey's armed forces, the second largest in NATO, were long the guardians of the secular republic established by Mustafa Kemal Ataturk, carrying out three coups between 1960 and 1980 and pushing an Islamist-led government from power in 1997.
Since first coming to power in 2002, Erdogan's Islamist-rooted AK Party has reined in army influence with a series of reforms designed to boost democracy, while prosecutors have pursued suspected coup-plotters in the army through the courts.
The latest verdict underlines the extent to which Erdogan has brought the military to heel during his decade as prime minister, consolidating his power as he prepares for an election cycle starting next year which could see him become president.
In a packed courtroom, supporters of the defendants noisily voiced their anger at the upheld convictions as the chief judge spoke, chanting the secularist slogan "we are Mustafa Kemal's soldiers" and "Tayyip will answer to the people".
Dozens protested outside the court, waving Turkish flags adorned with Ataturk's picture. "We know well it is Ataturk being tried," said one banner held by the group, which then marched to Turkey's military headquarters before dispersing.
Defence lawyer Celal Ulgen said the court had accepted fabricated evidence as genuine and that the judiciary in Turkey was subject to political manipulation.
"They want to redesign Turkey with these political trials," said Ulgen, who defended chief suspect Cetin Dogan.
"This is the dissolution of the (Turkish) Republic and a fundamental indication that we are faced with a new regime," he said, vowing to challenge the verdicts at the European Court of Human Rights.
The appeals court upheld 20-year prison sentences for chief suspect Dogan, a former commander of the prestigious First Army, former air force commander Ibrahim Firtina and retired admiral Ozden Ornek, court chairman Ekrem Ertugrul said.
Among other leading figures whose convictions were upheld were Engin Alan, a retired general elected to parliament as a member of the National Movement Party in 2011, and retired general Bilgin Balanli, who had been in line to become air force commander before his arrest.
In total, the court upheld convictions in the three-year trial process of 237 defendants and ruled in favour of the release of 88 defendants. It also upheld the previous acquittal of 36 defendants.
Opposition MP Emine Ulker Tarhan echoed Ulgen's allegation that the court ruling was politically motivated.
"This is not a verdict by the judiciary, it is a government verdict. Justice has collapsed in this country. They can build a shopping mall in its place," Tarhan told reporters, playing on accusations that the government is more focused on superficial projects than substantive reforms.
There was no immediate government comment on the verdicts but Mustafa Varank, an advisor to Erdogan, wrote on Twitter: "Hopefully the rulings will be a lesson and the coup word will not even cross anybody's mind".
Sledgehammer and other trials have sparked accusations that the government was using courts to silence political opponents and rights groups have criticised the number of journalists, lawyers and politicians held in jail pending verdicts.
A separate Turkish court in August jailed a former military chief for life and imprisoned scores of other leading figures in connection with the separate Ergenekon conspiracy to overthrow the government.