A Portland couple arranged to trade marijuana for the chance to have sex with a 5-year-old girl, the authorities said Tuesday.

Federal agents arrested Christopher Dudley, 27, and Rhea Hamm, 22, in Woodland, Wash., where they were to meet the girl — a fictitious character created by an agent who met Dudley in an Internet chat room.

Dudley and Hamm were charged with aggravated sexual abuse of a minor.

Special agents made the arrests as part of an undercover Internet sting designed to catch online sexual predators, said Lorie Dankers, a spokeswoman for U.S. Immigration and Customs Enforcement.

Senior Agent James Mooney conducted the sting last month in a chat room known to trade in images of young girls engaging in sex, according to court papers. Mooney posed as the father of a 5-year-old girl.

In a series of e-mail chats with the agent, Dudley allegedly agreed to pay the father so that he and Hamm could perform oral sex on the child and take photos.

According to court papers, Dudley described himself during the chat as a "decent" person with a "weird" fetish. When the agent expressed surprise that Dudley's wife would take part, Dudley typed that he told Hamm before they were married about his interest in young girls. Dudley said he was trying to scare her off, "but she said she loved me and didn't care what I was into."

An undercover agent then had two phone conversations with Dudley, who allegedly detailed prior sexual contact with an 8-year-old girl. Moreover, Dudley said that he and Hamm were trying to have a daughter and wanted her to live the "lifestyle."

The agent later met the couple at a Denny's in Portland. Court papers say the agent told Hamm that she should not take part in the sexual encounter if she was only doing so to please someone else. Hamm allegedly told the agent that she wanted to do it.

On Monday, the agent called Hamm and Dudley and told them he was traveling south from Tacoma with child. An Econolodge was the chosen meeting place.

Dudley and Hamm were arrested after taking the motel exit. Agents seized marijuana from the car, as well as a digital camera, a vibrator and $108, court papers say.

Investigators said Dudley and Hamm agreed to be interviewed after their arrests, and both acknowledged planning to have oral and genital contact with the girl.

"This case shows the extraordinary lengths some adults will go to sexually exploit innocent children," said Mike McCool, deputy special agent with the Seattle office of U.S. Immigration and Customs Enforcement.