Opposing attorneys agreed Friday that Elizabeth Smart should be allowed to testify about the facts of her abduction -- a nine-month ordeal prosecutors say was propelled by Brian David Mitchell's desire for sex rather than his religious belief in polygamy.

But defense attorney Robert Steele said Smart, as a lay person, should not be allowed to offer opinions about what motivated Mitchell's behavior nor whether he appeared to be mentally competent.

"What we object to are the opinions that go to state of mind," said Steele at a federal court hearing.

Assistant U.S. Attorney David Backman countered that Smart was with Mitchell "24/7" for months and can provide important observations.

"She would testify that what preoccupied him was sex. That's what drove him," the prosecutor said.

Backman said Mitchell -- a self-proclaimed prophet who allegedly wanted the then-14-year-old Smart as a plural wife -- has refused to cooperate with the mental health experts who have examined him and might be able to trick even them. Smart is "much more equipped to see how the defendant acts when he's not under the microscope," Backman argued.

U.S. District Judge Dale Kimball said he will decide early next week if Smart can testify and whether her testimony could include her opinions of Mitchell's mental state, such as whether he was "distressed" at times.

Mitchell began singing a Mormon hymn as he was brought into the courtroom on Friday, as he has at many other hearings. After he ignored Kimball's order to stop, he was taken to another room where he could see and hear the proceedings without disrupting them.

Backman said Mitchell is able to behave appropriately in a courtroom when it serves his purpose and cited as an example his arrest in February 2003 after breaking into a Lakeside, Calif., church. Mitchell entered a guilty plea and was sentenced to six days in jail.

"The defendant can come into court and not sing," Backman said, adding that Mitchell told Smart "all about" that appearance.

After the hearing, Smart's father called Mitchell "a total manipulator."

"I think it's outrageous that he could be considered incompetent because he won't cooperate (with the mental health experts)," Ed Smart said. "He knows exactly what he's doing."

Smart's testimony would be part of a larger hearing to determine if Mitchell is mentally competent to stand trial on federal charges of kidnapping and coercion or enticement of a minor with intent to engage in sexual activity. If the judge decides Smart, who is now 21, can testify, she will do so at a hearing scheduled for Thursday.

On Nov. 30, Kimball will hear from both prosecution and defense witnesses about whether Mitchell is able to understand the charges against him and can assist in his defense. Smart's testimony would be taken early because she is entering language training next month in anticipation of going on a Church of Jesus Christ of Latter-day Saints mission to Paris.

The prosecution has 39 lay people and four experts listed as potential witnesses but says that number will be honed down. Friday's arguments concerned only Smart's testimony.

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