WASHINGTON/SAN FRANCISCO, June 21 (Reuters) - Twelve of the 14 judges who have served this year on the most secret court in America are Republicans and half are former prosecutors.

One is a former director of the Illinois State Police. Another helped direct the White House war on drugs. One served as a prosecutor in the Whitewater case involving the Clintons’ real estate investments. Another forced President Bill Clinton to testify during the same scandal.

But judges of the Foreign Intelligence Surveillance Court, drawn from regular trial courts across the country, also have issued orders in public cases that belie their conservative, law-enforcement roots, sometimes ruling against the government in terrorism-related cases.

Years after the drug official - Reggie Walton - left George W. Bush’s White House, he sentenced Scooter Libby, Vice President Dick Cheney’s chief of staff, to 30 months in prison for perjury. And years after Bush appointed the Whitewater prosecutor - John Bates - to the federal bench, he declared part of a law on military commissions unconstitutional.

The trial court judges who sit on the FISA court wield great power working in secret. The court has come under scrutiny after Britain’s Guardian newspaper published details of a secret FISA court order requiring Verizon Communications to provide data to the NSA.

While U.S. intelligence officials have insisted that the FISA process is thorough, little attention has focused on the judges themselves.

Selected by the Chief Justice of the Supreme Court, FISA judges serve for staggered seven-year terms. Although the court carries 11 judges at a time, 14 have served this year because of routine turnover.

Six of the 14 were originally appointed to the trial courts by George W. Bush; five by Ronald Reagan; two by Clinton and one by George H. W. Bush.

“Since FISA was enacted in 1978, we’ve had three chief justices, and they have all been conservative Republicans, so I think one can worry that there is insufficient diversity,” said Stephen Vladeck, a law professor at American University’s Washington College of Law.

WINDOWLESS COURTROOM

Every few months, the FISA judges set aside their regular, public cases, travel to Washington, and take the bench inside a secure, windowless courtroom at 333 Constitution Avenue. Prosecutors and federal agents appear to answer questions about warrants before individual judges, rather than a panel.

Generally, the judges rotate on a week-long schedule. Three judges live in the Washington area and are available for emergencies. FISA judges do not receive extra pay.

Walton, the senior judge on FISA, declined to be interviewed. In a statement, he said: “The perception that the court is a rubber stamp is absolutely false. There is a rigorous review process of applications submitted by the executive branch, spearheaded initially by five judicial branch lawyers who are national security experts, and then by the judges, to ensure that the court’s authorizations comport with what the applicable statutes authorize.”

The other FISA judges who served on the court this year either declined to comment or did not respond to queries for comment.

What little is known about the court’s current business can be gleaned from statistics disclosed in annual two-page reports to Congress.

Between 2001 and 2012, the FISA judges approved 20,909 surveillance and property search warrants - an average of 33 a week. During that 12-year period, the judges denied just 10 applications. Prosecutors withdrew another 26 applications.

From 2007 to 2012, FISA judges also approved 532 “business record” warrant applications, the category used in the order that directed Verizon to release metadata on all phone calls inside the United States. No business record warrants were rejected.

The records also show that FISA judges ordered “substantial modifications” to 497 surveillance and property warrants and 428 of the business record warrants.

The statistics are especially intriguing for business record warrants for 2011 and 2012. Of 417 warrants authorized, the court “substantially modified” 376.

Yet details are classified, so it is unknown exactly how the judges modified the warrants.

In rare public remarks 10 years ago, a former presiding FISA judge, Royce Lamberth, described the process: “I ask questions. I get into the nitty-gritty. I know exactly what is going to be done and why. And my questions are answered, in every case, before I approve an application.”

Syracuse University College of Law professor William C. Banks, who follows the FISA court closely, said he suspects that warrants are “modified” when judges request more information about a warrant or decide to split a warrant with multiple suspects, phone numbers and locations into several, more specific ones.

“We can’t tell the extent of modification, but clearly it suggests that the judges are taking a real look at these things and are at least modifying them in some respect,” said Penn Law professor Theodore Ruger. “But I don’t think it answers the bigger, more important question of whether this court is acting as a balanced check on the government’s authority.”

Ruger studied selections made by the previous chief justice, William Rehnquist, and found that he selected mostly conservative, Republican judges, reflecting the general population of trial-court judges at the time. Today, the federal judiciary carries a more even Democratic-Republican split, Ruger said, but the FISA court remains dominated by Republicans.

“The judges are hand-picked by someone who, through his votes on the Supreme Court, we have come to learn has a particular view on civil liberties and law enforcement,” Ruger said. “The way the FISA is set up, it gives him unchecked authority to put judges on the court who feel the same way he does.”

John Roberts, who has been Chief Justice of the Supreme Court since 2005, declined to be interviewed.

On May 20, an exclusive group met in Washington for a private dinner sponsored by the American Bar Association. Current and former members of the FISA court convened to celebrate its 35th anniversary.

Banks, the Syracuse professor, gave a keynote speech in which he lamented post 9/11 changes, including the 2008 amendment permitting broad surveillance.

“FISA envisioned case-specific surveillance, not a generic surveillance operation, and its approval architecture was accordingly geared to specific, narrowly targeted applications,” Banks told the FISA judges, according to a transcript. The 2008 changes to the law, he said, have “strained its utility as an independent arbiter of lawful FISA surveillance.”

The FISA court, he told the judges, had evolved into an administrative, rather than a judicial, body. His remarks received polite, if tepid, applause, he recalled.

Two weeks later, The Guardian made public the top-secret Verizon order.

Below are further details on some of the judges.

* Reggie Walton, the current FISA presiding judge, may be best known for two high-profile perjury trials - the one with Libby, who was ultimately pardoned by Bush and another against former baseball pitcher Roger Clemens. Walton declared a mistrial in Clemens case after the government improperly presented evidence and on retrial the athlete was acquitted. Lawyers say Walton is a stern judge at sentencing, but note he has also chaired the national prison rape commission. “He’s pro-government, but I don’t think he’s pro-government in terms of doing reflexively what the government wants,” a defense lawyer wrote of Walton in an anonymous survey published by the Almanac of the Federal Judiciary.

* James Zagel, who led the Illinois State Police for seven years, co-authored widely-used law school text books on criminal procedure, wrote a critically-acclaimed crime novel, presided over the corruption trial of former Illinois Governor Rod Blagojevich and appeared as an actor in a 1991 David Mamet movie, ‘Homicide.’ “He leans slightly toward the government,” a defense attorney wrote in the Almanac survey.

* Roger Vinson of Florida, who signed the Verizon order, is perhaps best known for striking down the Obama Administration’s health care law in 2011. He declared the Affordable Care Act’s individual mandate unconstitutional and federal government overreach. The Supreme Court, led by Roberts, disagreed. Vinson’s seven-year term on the FISA court expired in May.

* John Bates of Washington, D.C., the judge who served as a Whitewater prosecutor, has dealt blows to the Obama administration in rulings on the indefinite detention of terror suspects. In 2009, Bates ruled that to be held at Guantanamo Bay indefinitely, a detainee must be a member of Al Qaeda, the Taliban or associated groups or have committed belligerent acts. Simply supporting those organizations, he ruled, is not enough. Bates’ term expired in February.

* Mary A. McLaughlin of Pennsylvania is the sole Democrat. She spent three decades working for white-shoe law firms and four years as a prosecutor. In 1995, McLaughlin served as a special counsel to a U.S. Senate subcommittee investigating an alleged FBI cover-up following a fatal shoot-out in Ruby Ridge, Idaho. The Almanac reports that defense lawyers describe her as fair and, as one said, “right down the middle on everything.”

* Martin Feldman of Louisiana was active in Republican politics from the Eisenhower to Reagan Administrations. He counts as a mentor and clerked for the liberal Republican John Minor Wisdom, an appeals judge credited with issuing significant civil rights rulings during the 1960s. An expert in tax and business law, Feldman most recently presided over litigation related to the Deepwater Horizon/BP oil spill.

* Raymond Dearie of New York, a veteran prosecutor, was described in the Almanac survey by defense attorneys as fair. “He has no leanings,” one reported.

* Thomas Hogan of Washington, D.C. has been involved in several high-profile cases, including a ruling that restricted public access to White House records kept by President Richard Nixon, an order requiring the Library of Congress to keep publishing a Braille version of Playboy for the blind and a decision that directed the government to stop routinely denying security clearances to naturalized Americans born in certain countries.

* Susan Webber Wright of Arkansas is best known as the judge who presided over the sexual harassment case Paula Jones filed against Clinton. Wright ruled that Clinton could postpone the lawsuit until after he left office, but the Supreme Court disagreed. She later held Clinton in contempt of court for lying under oath about a sexual encounter with White House intern Monica Lewinsky.