WASHINGTON – The treatment to restore mentally unfit defendants to competence so that they can stand trial for heinous crimes is an uncertain science that, in a number of high-profile cases, has taken years – and at times failed altogether.

Legal and medical experts said the odds are good that Jared Lee Loughner, 22, ruled incompetent by a federal judge this week, will recover though antipsychotic drugs and ultimately face charges in the Jan. 8 shooting spree in Tucson, Ariz., that killed six and wounded Rep. Gabrielle Giffords, D-Ariz., and 12 others.

But the experts also cautioned that significant pitfalls could prevent a speedy trial.

Each year, an estimated 10,000 to 12,000 defendants across the country have their trials delayed after being found mentally incompetent. Roughly 75 percent are successfully rehabilitated within six months, according to several published studies.

Those who do not recover quickly, however, often remain in a lengthy state of limbo, even though the U.S. Supreme Court has ruled that defendants cannot be held indefinitely. For example, Lucas John Helder, 30, accused of planting bombs in 18 mailboxes across the Midwest in 2002, has remained in a federal medical facility in Rochester, Minn., since April 2004, when a judge found him incompetent.

“There is a subset that for various reasons do not respond,” said Kirk Heilbrun, chairman of Drexel University’s psychology department, who has worked with juvenile and adult offenders. “They don’t respond as well to the medication, or it’s not the right medication or dosage. There could be issues about their motivation, such as they exaggerate or fabricate symptoms, and it can be hard to document.”

Mental incompetence, unlike an insanity defense, is based on the defendant’s state of mind heading into a trial. An insanity defense focuses on the defendant’s mental health leading up to the crime and during it. Legal experts said they expect Loughner’s attorneys to present an insanity defense if he goes to trial.

But such cases are rarely successful and have become even more difficult since Congress tightened the insanity-defense standards after John Hinckley Jr., who shot President Ronald Reagan, was found not guilty in 1982.

For the next four months, Loughner will spend his nights in a sparsely furnished cell at the 300-inmate psychiatric wing of the U.S. Medical Center for Federal Prisoners in Springfield, Mo.

U.S. District Judge Larry Burns, who ruled Loughner mentally unfit, has set a Sept. 21 date in a Phoenix federal courthouse to determine whether he has recovered or is making enough progress to continue the rehabilitation.

Physicians will seek to administer drugs such as Abilify, Seroquel, Risperdal or Geodon to control his diagnosed schizophrenia, and staff psychologists and psychiatrists will work with Loughner daily, said David Mrad, a forensic psychologist who worked at the Springfield facility for 24 years before retiring in 2006.

Patricia Zapf, an associate professor of forensic psychology at John Jay College in New York, said defendants who fail to recover their mental competence usually fall into two categories: those with a severe brain injury or mental retardation and those who have exhibited a long history of severe mental illness.