Whether the Secretary of the Interior's longstanding interpretation of Executive Order No. 8979 and Public Land Order No. 487 was entitled to judicial deference.
Holding
Yes. The Secretary's interpretation was reasonable, consistently maintained, and entitled to controlling weight because it was not plainly erroneous or inconsistent with the orders.
Reasoning
The Court distinguished between ordinary statutory interpretation and interpretation of an agency's own regulatory or administrative instruments. Where the meaning of an administrative order is doubtful, the agency's interpretation ordinarily controls unless it is plainly erroneous or inconsistent with the instrument. Here, the disputed Public Land Order was issued by the Secretary, and the President had delegated to the Secretary broad authority to modify or revoke public-land withdrawals.
The Interior Department had consistently treated the orders as permitting oil-and-gas leasing subject to appropriate conditions. It accepted lease applications, processed earlier applications after policy suspensions ended, approved leases in the Moose Range, and publicly defended that position before Congress. This was not a post-litigation construction devised for the case; it was a settled administrative practice predating respondents' applications.
The longstanding practice also carried practical significance. Hundreds of leases had been issued in the affected area, and lessees had spent tens of millions of dollars developing them in reliance on the Department's view. Respondents, by contrast, could not claim detrimental reliance on a contrary interpretation. The Court therefore found no cogent reason to displace a publicly known and consistently applied administrative construction.