Wausau Benefits, a Wisconsin company that manages health care benefits for companies, has bought a Des Moines-based unit from insurance giant Marsh & McLennan Cos.     Roughly three-quarters of the 230 workers in the unit, which handles health-care-related administrative tasks for retirees, could lose their jobs as a result of the acquisition. The purchase price was not disclosed.

Wausau intends to hire about 60 workers in Des Moines and an undisclosed number in Wausau, Wis., according to Susan Ford-Hoffert, a Wausau spokeswoman. The company said it will sub-lease about 16,000 square feet of office space from Marsh in the Riverpoint Business Park, where the Marsh unit is currently located.

Marsh, which employs about 2,000 people in Des Moines, intends to hire some of the displaced workers for other jobs that it has available here, according to Monica Green, a Marsh spokeswoman. Marsh became a major Des Moines employer in 1998 when it bought Kirke-Van Orsdel Inc.

All of the affected workers will keep their jobs through the end of the year, and many will continue working past December through contracts that last “several months into 2003,” Green said.

Marsh won’t know how many people it will hire until Wausau finishes hiring all the workers it needs to run its Des Moines office, Green said.

“We can’t assess our needs until we know exactly what Wausau is going to do,” Green said.

The acquisition gives Wausau, which two years ago spun itself off from Liberty Mutual Group in a management-led buyout, a chance to boost its presence in the market for managing retiree benefits.

The purchase also gives Wausau a third claims operation. It now operates claims offices in Wausau and Tampa, Fla.