CENTENNIAL, Colo. (Reuters) - A Colorado judge presiding over the case of accused theater gunman James Holmes entered a not guilty plea on his behalf on Tuesday to charges he went on a shooting spree in a Denver suburb nearly eight months ago and killed 12 moviegoers.

Arapahoe County District Judge William Sylvester made the move after declining a defense request for a continuance, paving the way for a trial to potentially begin in August. Holmes' lawyers said the defense was not ready to enter a plea.

Holmes faces multiple counts of first-degree murder and attempted murder stemming from the July 20 rampage that also wounded 58 people and was one of the deadliest mass shootings in U.S. history.

"This matter has been pending since July 2012," Sylvester said. "I acquiesced to the defense and put off the date as long as we could."

Holmes, who has grown shaggy hair and a beard since his arrest, glanced briefly at his parents as he entered a courtroom on Tuesday that was also packed with survivors or people who lost family in the shooting.

His lawyers are expected to mount an insanity defense for the former University of Colorado neuroscience graduate student who surrendered to officers outside the theater in the Denver suburb of Aurora within minutes of the mass killing.

Prosecutors have depicted Holmes, 25, as a young man whose once promising academic career was in tatters. He failed graduate school oral board exams in June and one of his professors suggested he may not have been a good fit for his competitive doctoral program, prosecutors said.

Arapahoe County District Attorney George Brauchler said in court that his office would announce at some point during court hearings in the first week of April whether it will seek the death penalty for Holmes.

Sylvester said that, even though he was entering a simple not guilty plea on Holmes' behalf, the defense could later substitute a plea of not guilty by reason of insanity. Sylvester also scheduled a four-week trial for Holmes to begin on August 5.

WOUNDED MAN

Marcus Weaver, who was wounded in the theater shooting, attended the court hearing and said afterward he was worried about a drawn-out legal proceeding if Holmes' defense team mounts an insanity defense.

"If he carries this out all the way, we should seek the death penalty," Weaver said outside the courtroom.

When Holmes' defense team asked to postpone the arraignment, some of those in attendance gave audible sighs in reaction.

The automatic plea by Judge Sylvester came a day after he ruled that Holmes could be medicated for psychiatric interviews and possibly face a polygraph test if he chooses to raise an insanity defense.

Holmes' lawyers have argued he should not be drugged while undergoing examinations by court-appointed psychiatrists.

During the hearing on Tuesday, Holmes' attorney Daniel King said the defense was still not ready for a plea because it was evaluating the ruling on psychiatric evaluations. King had sought to postpone the entering of a plea until at least May 1.

"If we enter a plea, the court will order a state evaluation and our evaluation would be truncated and cut short," King said.

Former Denver prosecutor Craig Silverman, who is not involved in the case, said he doubted the case will go to trial in August due to the legal issues that will be brought up surrounding an insanity defense and capital punishment.

"Today was not the first, or last time, defense attorneys will attempt to the delay the case," said Silverman, who won a death-penalty verdict as a prosecutor. "Every day the trial is delayed is another day the defendant stays alive."

Holmes' lawyers unsuccessfully sought earlier this month to have the state's insanity-defense law declared unconstitutional by arguing it requires defendants to incriminate themselves to court-appointed psychiatrists.

Defense attorneys also revealed in pleadings released last week that Holmes spent several days in a psychiatric unit in November, frequently in restraints, because jail officials believed he was a danger to himself.