The arrests of 219 people in a sweeping, two-year investigation is part of a struggle for control in Turkey, where an elected government run by pious Muslims is undermining military-backed elites that owned the country after Mustafa Kemal Ataturk, a war hero, created a secular state out of chaos in 1923.

On March 10, prosecutors filed a second indictment in the case against Ergenekon, an ultranationalist gang that takes its name from a legendary valley in Central Asia thought to be the ancestral homeland of Turks.

Suspects include academics, journalists, businessmen, retired generals and a few active-duty officers, most of them known to be secular-minded foes of Prime Minister Recep Tayyip Erdogan.

One of those detained on allegations of links to Ergenekon was Mustafa Balbay, the chief journalist in Ankara for Cumhuriyet, a secular newspaper critical of the government.

Reporters Without Borders, a Paris-based group, said there was "so far no evidence" against Mr. Balbay amid concerns that prosecutors were casting their net too wide and could undercut their own credibility.

Prosecutors accuse suspects of seeking to foment chaos and compel the military to take over in a manner similar to coups that ousted less stable, civilian governments. Ergenekon is seen as the remnants of the "deep state," a term for state-linked networks whose purported slayings and abductions peaked at the height of a Kurdish rebellion and Cold War-era rifts.

Hugh Pope, Turkey project director for the International Crisis Group, praised the push for "accountability" as overdue in a nation whose government has strong public support, but where the military remains a powerful, behind-the-scenes force in politics.

"This is very close to the bone in Turkey," Mr. Pope said. "Both sides are moving in such ways not to push the other one over the edge."

The military appears to be cooperating, and the justice minister recently visited the armed forces chief in what commentators interpreted as an attempt to smooth tension over questions about military involvement in the suspected conspiracy. Turkish media said the new indictment includes charges that several military commanders plotted a coup in 2004.

Those allegations emerged in 2007 in Nokta, a weekly magazine that published excerpts from a diary that it said belong to Adm. Ozden Ornek, who retired. The diary reports on plans for coups code-named "Blonde Girl" and "Moonlight" that were abandoned, partly because of a lack of support from other commanders.

Nokta closed soon after a police raid on its offices. Adm. Ornek denied he wrote the diary.

The Ergenekon gang is suspected in attacks on a newspaper and a courthouse, and plots to kill the prime minister and author Orhan Pamuk, Turkey's Nobel laureate. The crackdown led to the overnight detention this month of Mehmet Ulger, commander of paramilitary forces in Malatya, when three members of a Christian publishing house were killed there in 2007.

Mr. Ulger was interrogated but not charged. A court ordered him not to leave Turkey, the Anatolia news agency reported.

The first, 2,455-page indictment was completed on July 10, more than a year after the investigation began. The probe followed the seizure of hand grenades at the Istanbul home of a noncommissioned officer. The second indictment seeks life in prison for two former generals, Hursit Tolon and Sener Eruygur, on charges of plotting to overthrow the government.

Burhan Kuzu, a ruling party lawmaker and head of Parliament's Constitutional Commission, said he was shocked by the breadth of the purported conspiracy, apparently aimed at creating an image of Turkey as ungovernable and at the mercy of Muslim extremists.

"The Ergenekon picture gives goose bumps," Mr. Kuzu said. "If these allegations are really based on evidence, then many unsolved murders will come to light."

The trial of Ergenekon suspects, which began in October, is part of a larger but limited effort to investigate crimes that may have involved state agents during more turbulent times. Authorities have begun digging at wells and other sites in southeastern Turkey in search of mass graves of Kurds who disappeared in the 1990s.

The ballooning size of the Ergenekon case has drawn accusations that the government is lumping political opponents with genuinely suspicious characters in order to silence criticism that it seeks to impose Islam on society.

"You cannot lead an investigation by mixing what is true with what is imaginary. The judiciary cannot reach a healthy decision in this way," said Senal Sarihan, a prominent secularist lawyer.

Some aspects of the Ergenekon trial - including accusations of unauthorized wiretapping, sweeping charge sheets and large numbers of defendants - recall mass cases against leftists and other dissidents after a 1980 military coup.

"Turkey has to be very wary of being seen to be going back to authoritarian ways," Mr. Pope said. "If it gets too broad, and it loses public support, then that's a bit of a threat to the process."