The Obama administration will make changes to the rules that govern the sale of ivory and horn antiques. The rules will ban commercial trade of elephant ivory by prohibiting its import, export and resale within the United States, with a few exceptions.

The steps are part of a broad effort announced recently by the White House to stem a global boom in wildlife trafficking that threatens species such as the African elephant and the rhinoceros with extinction.

Under the existing system, ivory cannot be imported unless it is an antique. Commercial objects made before 1976 and antiques can be exported, and domestic sales are essentially unregulated.

The new measures also will ban the import of antique African elephant ivory and all exports, except antiques.

The administration will ban the resale of elephant ivory across state lines, except antiques. Sales within a state will be prohibited unless the seller can demonstrate an item was lawfully imported before 1990 for African elephants and 1975 for Asian elephants. People can still own ivory and pass heirlooms to descendants, officials said.

To qualify as an antique under the new measures, an item must be more than 100 years old and meet other requirements under the Endangered Species Act, criteria that sellers will have to demonstrate.

The biggest change will be that law enforcement will no longer have to prove that ivory it seized was illicitly acquired. Owners now have the burden of proof to show they legally obtained it.