WASHINGTON — A top American diplomat signaled on Thursday that the United States might no longer demand that North Korea turn over a complete inventory of its nuclear assets as a first step in the denuclearization process that President Trump is pursuing.

The diplomat, Stephen E. Biegun, said in his first public speech that “before the process of denuclearization can be final, we must have a complete understanding of the full extent of the North Korean W.M.D. and missile programs through a comprehensive declaration.”

Mr. Biegun, appointed in August to be special representative for North Korea, was speaking to a room of North Korea experts at Stanford University. His reference to the timing of North Korea’s releasing a full list of its weapons of mass destruction indicates that the United States could be more flexible than it previously indicated about at what point in the negotiations the list is handed over.

If American negotiators drop their demand that the list is an essential first step in denuclearization, that would remove one obstacle that has hampered diplomacy since a summit meeting last June between Mr. Trump and Kim Jong-un, the North Korean leader.