WASHINGTON — The Justice Department has declared that the Food and Drug Administration lacks legal authority to regulate drugs that are used to carry out lethal injections, opening the door for states to import scarce death-penalty drugs even if the agency has not approved their use.

In a 26-page memo signed on May 3 and quietly posted Tuesday evening on the Justice Department’s website, Steven A. Engel, the head of the department’s powerful Office of Legal Counsel, concluded that the F.D.A. had no right to regulate death-penalty drugs because they do not count as a “drug” or a “device” within the meaning of the Federal Food, Drug and Cosmetic Act of 1938.

Under the act, drugs that alter or affect the body cannot be brought to market in the United States unless and until the F.D.A. has approved them as safe. But in a 2000 ruling, the Supreme Court held that the F.D.A. lacked authority to regulate tobacco because it could not be used safely and yet there was no sign that Congress had intended for it to be banned.

Relying heavily on the exception the Supreme Court carved out in that ruling, Mr. Engel said that death-penalty drugs similarly do not come under the agency’s control.