By Daren Butler

ISTANBUL (Reuters) - Prime Minister Tayyip Erdogan said Turkey was drowning in waves of arrests of military officers accused of coup conspiracies and called for the investigations, which his government has backed, to be wrapped up more quickly.

Around 50 retired and serving officers, some very senior, have been held over the last month in raids linked to the 1997 toppling of Turkey's first Islamist-led government. The arrests run parallel to trials of hundreds of officers, businessmen and academics accused of involvement in other alleged coup plots.

"These (waves of police raids) disturb the social peace. We too are seriously uneasy about this," Erdogan told reporters on Tuesday night on his return from a visit to Italy.

"The necessary steps should be taken and finished before moving on. But when these waves come one after the other, the country is drowned in those waves. I don't think this business should be dragged out this much," he added.

Erdogan, viewed in the army and old secularist establishment with suspicion because of his Islamist past, has promoted the trials as part of the process of ending the political power of the generals, who toppled four governments in the second half of the 20th century. He has also set about reforming a conservative judiciary, in part hostile to him, since first elected in 2002.

Critics accuse him of persecuting the armed forces and 'settling scores', undermining the secular foundations of the country. Many suspects have been held for months or even years in pre-trial custody.

INTERNATIONAL OPINION

The investigation into the events of 1997, known as the "post-modern coup" for its bloodless nature in contrast to other actions, has special significance for Erdogan who was a member of Erbakan's party.

He welcomed the investigations last month, saying "Turkey would never again be a country where those who get up early carry out coups."

Veteran commentator Mehmet Ali Birand said that f or all desire to reach legal closure on painful periods of Turkey's history, shortcomings in the judicial system were slowing, and undercutting public support for, t h e process.

"They know that the more they drag their feet, the more it will be difficult to satisfy public opinion," Birand told Reuters. " Because of the inadequacies of the judicial system, they are losing international public opinion as well."

On Tuesday, police, armed with arrest warrants for 17 officers, detained the Third Army chief of staff Major General Berkay Turgut among 10 active and retired generals targeted in a fourth wave of raids in a month.

Around 40 suspects were already in pre-trial detention, notably including Cevik Bir, a retired general who is chairman of Turkey's army pension fund, and retired lieutenant-general Yildirim Turker.

After years of tension, relations with the military have improved since Erdogan appointed General Necdet Ozel as armed forces chief last year. His appointment followed the resignation of top commanders unhappy with the conduct of an investigation into an alleged coup plot in 2003.

Some 365 officers, serving and retired, are currently being tried for alleged involvement in "Operation Sledgehammer". The prosecution says there was a plot to bomb mosques and tourist sites in Istanbul, assassinate members of religious minorities and provoke a near war situation with Greece as part of a plan to destabilize Erdogan's government.

(Editing by Simon Cameron-Moore)