WASHINGTON — Employees whose companies switch from traditional pension plans to an increasingly adopted alternative generally lose benefits, congressional auditors have found.

The report by Congress' Government Accountability Office, released yesterday, adds to the debate over the nation's private pension system. For months, lawmakers have been grappling with an overhaul of the rules governing company pension plans as a number of big companies dump their troubled plans on the financially strapped federal agency that insures them.

Democratic lawmakers, who last year asked the GAO to examine the matter, seized on the report as fresh evidence that the so-called cash balance pension plans hurt workers.

With cash balance plans, employees generally receive one lump-sum payment when they retire or leave the company.

The plans resemble 401(k) retirement plans in that they let workers track the growth of their money in a hypothetical individual account. Unlike 401(k) plans, however, employees in a cash balance plan can't allot part of their salary toward the plan or decide how it is invested.

Traditional pension plans reward workers for staying with a company; often it is in their last years in a job that their pension benefits increase the most. The cash balance plans usually save companies money because they can contribute less than they would under a traditional plan.

Critics of the plans maintain that they unfairly discriminate against older workers.

Many companies, including IBM and AT&T, have converted from traditional defined-benefit pension plans to cash balance plans in the last 15 years

The GAO auditors, who examined 31 large company plans and 102 smaller ones, found that when employers switch from defined-benefit pension plans to cash balance plans, "most workers, regardless of age, would have received greater benefits under the (defined-benefit) plan."

Also, unless older employees are given the right to remain in the traditional plan, they "experience a greater loss of expected benefits than younger workers," the report says.

It estimates the median loss in retirement benefits each month for a 30-year-old employee to be $59, rising to $188 for a 40-year-old worker and $238 for a 50-year-old.