* Agreement came days ahead of Monday hearing
* Lawyers say both parties wanted best for children
* Children benefit from estate, valued at $500 mln or more (Adds indefinite delay to toxicology report)
LOS ANGELES, July 30 (Reuters) - Michael Jackson's mother will get custody of the late pop star's three children after reaching an agreement with his ex-wife Debbie Rowe, avoiding a custody battle only days before a court hearing on the matter.
Rowe will have visitation rights with her two biological children with Jackson -- Prince Michael, 12, and Paris, 11, under the terms of the agreement, lawyers said on Thursday.
The biological mother of Jackson's third child, Prince Michael II, 7, also known as Blanket, has never been revealed.
Jackson's mother, Katherine, 79, was granted temporary custody of the children after he died from cardiac arrest on June 25.
The "Thriller" singer had stipulated in his 2002 will that he wanted his mother to care for the children, but following his death, Rowe seemed to consider challenging Katherine Jackson's custody. A hearing on the matter was set for Monday.
"Mrs. Jackson and the family are pleased this matter is resolved and was handled in a caring, thoughtful and courteous manner by the parties and their representatives," Londell McMillan, Katherine Jackson's attorney, said in a statement.
"We were all united in our goals to do what is best for Michael's wonderful children, and both Mrs. Jackson and Debbie Rowe were on the exact same page," McMillan said.
Eric George, an attorney for Rowe, said in a statement that the agreement was a "dignified outcome."
"The sole consideration between the parties was the best interests of the children," he said.
VALUE OF ESTATE
Jackson left his estate, valued at more than $500 million in an attachment to his will, to a family trust that benefits his children, his mother and charities.
"That estate is worth, in my estimation, a couple of billion dollars," McMillan said in an interview on CBS News' "The Early Show," referring to the future value of the estate if it achieves its potential earnings.
"You hear $500 million. Don't buy it," he said.
Estimates vary widely. Several recent reports including one in the Los Angeles Times have put a net value on the estate of $200 million.
The major portion is Jackson's part ownership in music publishing company Sony/ATV, which owns old Beatles tunes and hundreds of songs from other artists and has been estimated to be worth as much as $1 billion. The singer also was said to be as much as $500 million in debt when he died.
Since his death, Jackson's songs and CDs have seen a rebirth in popularity, and there is wide speculation about future DVDs, movies and TV projects in the works that could add value to the Jackson estate.
At the hearing on Monday, lawyers for Jackson's mother and executors named in the singer's will are expected to argue over the administration of his estate.
The coroner's report on the cause of the pop star's death is still awaiting toxicology and other test results.
The toxicology report had been expected as soon as this week, but a spokesman for the Los Angeles coroner's office said on Thursday it has been delayed indefinitely.
Los Angeles police with the help of U.S. drug agents are looking into whether doctors provided for Jackson powerful prescription drugs, including the anesthetic propofol, which could have led to his death.
Despite a public memorial for the singer earlier this month, Jackson's private burial arrangements still have not been announced and his body remains at a Los Angeles mortuary. (Reporting by Michelle Nichols and Alex Dobuzinskis; Editing by Bob Tourtellotte and Peter Cooney)
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