Hundreds of patent examiners appear to have cheated on their time cards yet were still rated as above average employees — and some were even given bonuses by their bosses at the U.S. Patent and Trade Office, the agency’s inspector general told Congress in devastating testimony Wednesday.

More than 100 examiners appeared to have ditched at least one full day’s worth of work each week, acting Deputy Inspector General David Smith said, adding that the agency, despite repeated warnings, still hasn’t figured things out.

The patent office pushed back, saying that while a few employees may be abusing the system, there’s no widespread problem among the 13,000 employees of the agency.

But the 400 worst employees, identified by statistical analysis, could have cost taxpayers $18 million in bogus pay and benefits — and that’s a conservative estimate, Mr. Smith told the House Oversight Committee.

“I guess it confirms what a lot of people think about the Washington, D.C., work ethic,” said Rep. Glenn Grothman, Wisconsin Republican.

None of the employees has been prosecuted, though Russell Slifer, deputy director at the office, said 30 of have been fired or faced other discipline because they were flagged for bad work.

The issue has bedeviled the PTO for years. One audit in 2015 found paralegals at the agency were directed by supervisors to falsify their hours, while another audit identified one examiner who likely bilked $25,000 worth of time in 2014 alone.

That examiner resigned in order to duck any consequences and to keep a clean record for future federal employment.

At the time, the patent office insisted it was taking steps to crack down — but the inspector general said they are still struggling.

“There’s still a lot of work yet to be done,” Mr. Smith said.

The Patent Office Professional Association, the labor union representing agency employees, dismissed the audit’s findings, saying it had a “flawed methodology.”

Pamela Schwartz, president of the association, said some examiners likely weren’t logged into their computers even though they were working that time. She also said examiners regularly work unpaid overtime to meet their production quotas, which more than compensates for the 2 percent of total time lost to bogus time claims.

Mr. Smith said he could get to the bottom of the issue if the association would encourage its members to voluntarily talk to his investigators.

“We would be more than happy to interview these employees,” he said.

He said they’ve come across online information where some examiners admitted they complete their work in less time than their superiors allot — but they claim the full time as worked.

Mr. Slifer said he wasn’t willing to trust that information, and insisted they don’t have a problem.

“I know that our examiners are working. I know, looking at our production requirements,” he said.