In a move designed to cut administrative costs by $16 million a year, the Interior Department has restructured the field operations of its Bureau of Indian Affairs.

But within hours of the announcement last week, the National Congress of American Indians condemned the plan, saying the agency did not adequately consult tribal leaders as required by law and Indian treaties.

Unless Congress disapproves, the reorganization will change the 12 BIA regional offices into five "service centers." The reshuffling will cost the government an estimated $7,045,000, mostly in severance pay.

Regional offices in Arlington, Sacramento and Muskogee, Okla., will be closed. Most of the 31 employes in the eastern regional office in Arlington will be asked to transfer to a new service center in Anadrako, Okla., while the rest will move to Interior headquarters. BIA offices in Minneapolis and Billings, Mont., will be downgraded in terms of responsibilities and staff size. Offices in Window Rock, Ark., and Juneau will become special program offices for the Navajo Nation and Alaska Native programs.

BIA will also operate service centers at Albuquerque, Phoenix, Aberdeen, S.D., and Portland, Ore.

Apparently bending to pressure from Republican senators, BIA decided not to move the Aberdeen office to Rapid City, S.D., as had been proposed. Vice President Bush announced that change a month ago, while the Indian groups thought their advice was still being sought. The department also dropped a plan to create a new office in Oklahoma City.

Sen. William S. Cohen (R-Maine), who chairs the Senate Select Committee on Indian Affairs, has scheduled a hearing on the reorganization for June 9.