The former business manager of Waipahu High School pleaded guilty Monday to stealing nearly $500,000 from the school under an agreement that could put him in prison for 18 months — or 10 years, depending on whether he pays the money back.

Warren Harada, 61, of Manoa pleaded guilty in state court to first-degree theft and four counts of money laundering.

New Principal Keith Hayashi’s scrutiny of purchases by Harada resulted in charges that the business manager stole $499,769 over a five-year period, said Christopher Young, supervising deputy state attorney general.

Harada spent some of the money on travel, including several trips per year to Las Vegas, a trip to Rome and one to Copenhagen, Denmark, Young said.

Harada has agreed to accept a five-year probation sentence, including 18 months behind bars. He also agreed to pay $25,800 in fines, court costs and fees at a rate of at least $650 per month, perform 1,000 hours of community service and write a letter of apology to the staff and students at Waipahu High.

Harada has until May 30, his date of sentencing, to repay the state $499,769. If he fails to pay the full amount by then, he will be sentenced to 10 years in prison instead of probation.

His lawyer, Scott Collins, said the extra three months from the originally proposed sentencing date in February should give Harada enough time to pay.

"We’re close to finalizing something in a short period of time," Collins said.

Young said Harada is selling some property that he hopes will cover the amount of the restitution.

"We are hopeful that Mr. Harada will fully honor the plea agreement and pay restitution in full," schools Superintendent Kathryn Matayoshi said in a statement Monday.

The $499,769 represents only the amount the state can prove in court Harada stole, Young said. The state audited $797,694 worth of purchases Harada made using school money from 2005 to 2010.

Harada returned some equipment, and investigators were able to locate $105,412 worth of equipment at the school. But they were unable to locate $192,512 worth of purchases, Young said.

"The basic scheme in this case was he’d use state purchase orders to purchase equipment, high-end equipment, and then he would find buyers to buy the equipment," Young said.

The equipment included cameras and laptop computers. The buyers were family friends, acquaintances and companies that resold them, Young said.