A former federal worker who persuaded employees nationwide to donate nearly 1,000 hours of their own paid leave so he could take time off for fictitious cancer treatments pleaded guilty to fraud Friday.

Robert Joseph Thom, 45, of Oceanside, admitted guilt for 10 counts of wire fraud that carry a combined sentence of up to 20 years in prison. He is to be sentenced Feb. 8 in U.S. District Court.

Thom was an information technology specialist with the U.S. Geological Survey in Southern California when he signed up nearly a year ago for a national donor list. He falsely claimed that he had undergone "multiple urgent surgeries for the removal of malignant tumors," according to court records.

He forged four letters from a doctor, all attesting to his ongoing medical problems, according to a September indictment.

A February letter claimed he needed more time off after developing infections. The last letter, in June, alleged that Thom had developed a malignant brain tumor.

Thirty Department of Interior employees responded to Thom's plea for help. They donated more than 982 hours of leave time with a value of nearly $40,000 so he could keep getting his salary and benefits while he was off work.

Donations came from Alabama, Alaska, California, Hawaii, Nevada, Oregon, Virginia and Washington, court records say.

It wasn't until August that the Geological Survey's Sacramento office sent Thom's doctor copies of the letters, according to an affidavit by an Interior Department investigator.

The doctor responded that the letters were "a complete and utter fraud," according to the affidavit. Thom was a real patient, but he had never been treated for cancer, the doctor told investigators.

His attorney, Dennis Waks, declined comment.

Prosecutors said Thom has agreed to make full restitution. He remains free on bond.

Thom, who was hired by the Geological Survey in 2004, is no longer a federal employee.