The Justice Department, again challenging the authority of an independent counsel, said yesterday that Whitney North Seymour Jr. has no right to compel the Canadian ambassador to testify at the perjury trial of former White House deputy chief of staff Michael K. Deaver.

The department, in an attack on the authority of the special counsel, maintained that diplomatic relations -- including the question of immunity for Ambassador Allan Gotlieb -- are best left to the executive branch, and Seymour's request to the court for a subpoena should be denied.

"It is necessary for the United States to appear in this proceedings and ensure that we abide by our international obligations," the department told U.S. District Court Judge Thomas Jackson, who is overseeing Deaver's pending trial for allegedly lying about his lobbying after leaving the White House.

Deaver, who faces trial on a five-count indictment, has twice claimed that Seymour is operating without constitutional authority, a view supported officially this week by the Justice Department.

Seymour contends Gotlieb waived his diplomatic immunity by agreeing to talk with investigators. That request, however, drew a formal protest from Canada and was spurned by the State and Justice departments, which filed the motion to quash the subpoena.