Military families have experienced “inordinate delays” getting medical-care referrals since UnitedHealth Group Inc. took over a Pentagon health contract, a U.S. defense official said.

The Minnetonka-based company last year wrested the contract, valued at as much as $20.5 billion, from TriWest Healthcare Alliance Corp. It assumed responsibility last month for the Western region of the military’s health care system, known as Tricare.

UnitedHealth’s “failure” has prevented a large number of beneficiaries in one Tricare health plan from obtaining timely access to specialty care, Jonathan Woodson, assistant secretary of defense for health affairs, said in a memo Thursday to other military leaders.

Woodson, calling the situation “extraordinary,” said the Pentagon stepped in to grant a temporary waiver so plan members in the Western region could get specialty care without UnitedHealth’s authorization and not incur penalties.

The delays are occurring because UnitedHealth has received requests for referrals and care authorizations that “far exceeded the norms” since it took over the contract, said Bruce Jasurda, a spokesman for the company.

“The increased volume was driven largely by people asking whether previously authorized referrals and authorizations were still valid, resulting in large numbers of duplicate referrals in the system,” Jasurda said in a phone interview. The company “understands the issues we need to improve on, and we are taking aggressive action.”

UnitedHealth has deployed additional staff to help process the increased number of requests, he said. It hopes to have the issues resolved in about a month, Jasurda said.

U.S. Rep. Doug Lamborn, R-Colo., told Defense Secretary Chuck Hagel that providers in his state are facing “unexpected and dramatic reductions in their workload” because of the backlog.