Elizabeth Smart would tell a court the former street preacher accused of abducting her was motivated by sex, not religion, if she is allowed to testify at his competency hearing, a federal prosecutor said Friday.

If Smart's testimony is allowed, it would be the first time she has faced Brian David Mitchell in court.

The 55-year-old who allegedly held Smart captive for nine months after kidnapping her in June 2002 has been diagnosed with a delusional disorder and was found incompetent to stand trial, along with his wife, Wanda Eileen Barzee. Both were charged with multiple felonies in state court in 2003, and last year a federal grand jury indicted the pair on charges of kidnapping and unlawful transportation of a minor.

Smart's father, Ed Smart, believes Mitchell's antics — singing in court and refusing to cooperate with psychiatric evaluators — are an act.

And Assistant U.S. Attorney for Utah David Backman said Friday that Elizabeth Smart would testify about how Mitchell acts "when he is not under the microscope" — that he was preoccupied and driven by sexual desire.

"We're pleading with the court to finally give Elizabeth Smart the voice she never wanted to have, but that Brian David Mitchell forced her to have," Backman told U.S. District Judge Dale Kimball Friday at a hearing on whether to allow Smart to testify. She is among 43 witnesses prosecutors have proposed putting on the stand.

Mitchell's federal public defender, Robert Steele, said he doesn't oppose Smart's testimony, but believes it should be limited to her experiences with Mitchell, not opinions about whether she believes he is competent.

Steele filed a motion Aug. 24 seeking to block any "lay witness," including family, friends, former church leaders and staff at state hospital, saying they are not qualified to assess mental competency.

Kimball said he is likely to rule on the issue Monday. A 10-day competency hearing is scheduled to begin Nov. 30.

Mitchell was accused of taking Smart, who was 14 when she was kidnapped, as a polygamous wife to fulfill a religious prophecy. She was found in March 2003, walking the streets of a Salt Lake City suburb with Mitchell and Barzee.

Smart, now 21, would testify early — at a hearing on Oct. 1 — because she is leaving in October to serve a religious mission for The Church of Jesus Christ of Latter-day Saints in Paris. Backman said he expected Smart would provide two hours of testimony.