HELENA, Mont. —  Attorneys reached a tentative plea agreement Friday in the case of a man charged with plotting to kidnap the young son of talk show host David Letterman (search), a prosecutor said.

Teton County Attorney Joe Coble told The Associated Press that Kelly Frank (search), who earlier pleaded not guilty in the case, was to appear Monday in state court in Conrad for a change-of-plea hearing.

Coble would not release details of the agreement, but said it was reached through Frank's attorney, Jim Hunt.

"We have a verbal agreement," Coble said. "We have presented a written agreement to the defendant, and he has it over the weekend to consider before he signs it."

Hunt did not immediately return phone calls seeking comment Friday.

Tom Keaney, spokesman for Letterman's production company, had not heard about the plea agreement and said no one was available to comment Friday evening.

Frank, who worked on Letterman's sprawling ranch near Choteau in northwestern Montana, was arrested in March after an acquaintance told authorities that Frank had talked of a plan to kidnap Letterman's then 16-month-old son, Harry Joseph, and the boy's nanny.

The acquaintance told authorities that Frank intended to hold the two for 48 hours on the belief he could extort $5 million ransom from Letterman.

Frank earlier pleaded not guilty to felony solicitation and theft and a misdemeanor charge of obstruction. He's been jailed since his arrest and has a July 18 trial date.

The theft charge accuses Frank of overcharging Letterman for painting work. The misdemeanor obstruction charge was filed after authorities said Frank initially lied to an investigator questioning him about a kidnapping plot.

Frank previously pleaded guilty to stalking and intimidating a woman who alleges he also kidnapped and raped her.