DENVER — The parents accused of pulling a spectacular hoax by reporting that their 6-year-old son had floated away aboard a helium balloon have agreed to plead guilty in a deal that could send them both to jail but protect the boy's mother from deportation.

Richard Heene will plead guilty Friday to attempting to influence a public servant, a felony, said his attorney, David Lane. Heene's wife, Mayumi, a Japanese citizen who could be deported if convicted of more serious charges, will plead guilty to a lesser charge of false reporting to authorities, a misdemeanour.

The Oct. 15 saga gripped a global audience, first with fear for the safety of 6-year-old Falcon Heene and then with anger at his parents when authorities accused them of perpetrating the hoax to drum up attention for a possible reality show.

Lane said the threat of deportation "fueled" negotiations with prosecutors. An attorney for Mayumi Heene said her immigration status was a factor in reaching the deal but would not comment further.

Prosecutors announced criminal charges against the couple Thursday. A spokeswoman for the Larimer County district attorney's office would not discuss whether a plea agreement had been reached.

Lane said the deal does not call for removing Falcon or the couple's other two children -- ages 8 and 10 -- from the parents' custody.

The plea deal would spare the Heenes the maximum jail time, but Richard Heene could still get up to 90 days and Mayumi up to 60, Lane said.

Without the deal, the charge against Richard Heene carries a possible sentence of two to six years in state prison and a fine of up to $500,000. The charge against his wife is punishable by up to six months in the county jail and a fine up to $750.

Mayumi Heene's attorney, Lee Christian, said he expects her to serve any jail time in a work-release program that would involve some detention and some time at home.

The parents still face a civil investigation by the Federal Aviation Administration. Possible penalties range from a letter of reprimand to a fine. The balloon briefly forced some planes to switch to a different runway for takeoff from the Denver airport.

Prosecutors said the Heenes agreed to turn themselves in and went to court Thursday to sign documents promising to appear before a judge on Friday. They held hands as they walked into the courthouse. The couple's children were not with them.

Richard Heene also had a booking photo taken at a county jail and was released. He declined to comment.

Lane said prosecutors insisted on a "package deal" that required Richard Heene to plead guilty to a felony so Mayumi Heene could plead guilty to a misdemeanour and avoid deportation.

"He feels like he's got to do what he's got to do to save his wife from being deported," Lane said.

On the day in question, the couple made frantic calls to authorities, saying they feared Falcon might be aboard a homemade balloon that had escaped from their backyard in suburban Fort Collins. That triggered a frenzied response by emergency crews before the balloon landed in a dusty farm field without the boy inside. The Heenes said they later found Falcon hiding at home.

Relief soon turned to suspicion. During a live interview on CNN hours after the balloon chase, Falcon looked to his father and said, "You had said that we did this for a show."

The Heenes' lawyers expect prosecutors to seek restitution in the case. Local and federal authorities spent at least $62,000 chasing the balloon and then searching for Falcon after it landed.

That price tag covers the cost of sheriff's deputies in two counties and military helicopters, but it's not clear whether there were any other agencies that also spent money on the effort.

Lane said he would fight any effort to recoup those costs.

The Heenes are amateur storm chasers and had twice appeared on the ABC reality show "Wife Swap." Former business partners said Richard Heene wanted a show of his own called "The Science Detectives" or "The Psyience Detectives."

Richard Heene, 48, denied the saga was a publicity stunt. Two days later, deputies questioned both parents separately, and authorities said Mayumi Heene admitted the incident was a hoax.

According to an affidavit, Mayumi Heene told an investigator the couple devised the hoax two weeks before the flight "to make the Heene family more marketable for future media interest." She said they built the balloon specifically for that purpose.

Mayumi Heene, 45, also said she and her husband had instructed their three children to lie to authorities and the media, the affidavit said.