WASHINGTON (AP) — It's the silent enemy in our retirement accounts: High fees.

And now a new study finds that the typical 401(k) fees — adding up to a modest-sounding 1 percent a year — would erase $70,000 from an average worker's account over a four-decade career compared with lower-cost options. To compensate for the higher fees, someone would have to work an extra three years.

The study comes from the Center for American Progress, a liberal think tank. Its analysis, backed by industry and government data, suggests that U.S. workers, already struggling to save enough for retirement, are being further held back by fund costs.

"The corrosive effect of high fees in many of these retirement accounts forces many Americans to work years longer than necessary or than planned," the report said.