HUDSON, N.Y., Sept 12 (Reuters)(CORRECTION) - Simon is only three years old but already an indispensable staffer at his office, where he has displayed a knack for helping abused children navigate an intimidating legal system.

He is also a lean, jet-black Labrador retriever.

Simon's job is to comfort children testifying or being interviewed in court cases, a normally stressful environment.

Diane Silman, Simon's boss as the head of the Ozark Foothills Child Advocacy Center in southern Missouri, said Simon has helped more than 300 children brave pretrial interviews, and accompanies them to court when necessary.

"A four-year-old once remained engaged in an interview for about an hour, which is pretty amazing," Silman said.

Dogs have been used to comfort victims and witnesses -- particularly children -- in and out of the courtroom for more than 20 years, and the practice has become relatively common in a handful of states over the last decade.

Until recently, courtroom dogs faced little more than preliminary objections from defense attorneys.

But earlier this summer, a New York lawyer became the first in the nation to appeal his client's conviction of raping and impregnating a 15-year-old girl because a dog was used to comfort her during her testimony at trial.

The girl testified with the aid of Rosie, a golden retriever who has worked with emotionally troubled children for years but was only recently recruited into the legal system.

Steven Levine, the lawyer who filed the appeal, said that the use of the dogs can affect testimony.

"The stress witnesses feel when they have to testify at trial tends to undo falsehoods," said Levine, a public defender in Poughkeepsie, New York. "Removing the stress deprives the defendant of a fair trial."

The judge's decision in the case, in which the alleged victim is the accused's daughter, will likely affect the courtroom use of the dogs nationwide.

Levine, several experts said, is the first attorney in the nation to appeal a conviction on the grounds that so-called comfort dogs could subconsciously sway juries and judges.

Their mere presence, Levine said, could imply to a juror that a witness is telling the truth "because you don't need to be comforted when you're giving false testimony."

But one of the early pioneers of using comfort dogs said Levine is "grasping at straws."

"The dog is not giving the witness the answers," said Andrew Vachss, an attorney who exclusively represents children.

He and his wife Alice, former head of the Queens District Attorney's sex crimes unit, first began using a dog to comfort traumatized children during interviews by prosecutors in 1987.

Vachss later donated a German shepherd to a Mississippi advocacy group and in 1992, that dog became the first in the nation allowed in a courtroom to comfort a witness.

In the case now under appeal, Vachss said he is confident the court will side with advocates of courtroom dogs, setting an important precedent.

There has been little controversy over courtroom dogs in states where the practice is more common than in New York.

In fact, Ramona Brandes, a public defender in Seattle, recalled a judge who wanted a dog present during a homicide trial to comfort everybody -- particularly the defendant, who Brandes said was disruptive but had a particular affinity for dogs.

Ultimately, the prosecutor rejected the judge's proposal.

Many nonprofit groups that provide dogs for legal proceedings take steps to ensure the animals are not disruptive in court.

"Generally we recommend they not be cute and cuddly and sit on the witness' lap," said Ellen O'Neill-Stephens, a Seattle prosecutor and founder of the advocacy group Courthouse Dogs.

The policy at Florida Four Legged Advocates is that dogs never join witnesses on the stand and stay out of the jury's line of sight.

"My priority is the child, and I would never want to do anything that puts a case in jeopardy," said FLA founder Andrea Cardona, whose dog Squiggly, a mixed golden retriever and yellow Labrador retriever, has worked on dozens of cases.

But Levine and lawyer David Martin, who represent the accused rapist, argue judges are creating law by allowing dogs in their courtrooms -- decisions better left to state lawmakers.

"If you want to use these dogs, go to your legislature, hold public hearings and then determine what's in the best interest of all the parties concerned," Martin said.

Levine said he does not expect a ruling on the appeal until next year at the earliest.

(Reporting by Dan Wiessner)

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(An earlier version of this story misspelled the name of Steven Levine. It's Steven, not Stephen.)