The official who oversaw a plan for the Pentagon to run a terrorist futures-trading market is resigning under pressure, a senior Defense Department official said today.

John M. Poindexter, a retired rear admiral who was President Ronald Reagan's national security adviser, is stepping down ''within a few weeks,'' the defense official said, after the disclosure of a proposal that outraged lawmakers and embarrassed senior Pentagon officials. The plan was to create an online trading parlor that would have rewarded investors who forecast terrorist attacks, assassinations and coups.

Defense Secretary Donald H. Rumsfeld did not personally fire Admiral Poindexter, but the defense official said that Mr. Rumsfeld agreed that the admiral had become too much of a political lightning rod and that it was time for him to go.

''It's fair to say that the secretary understood what Admiral Poindexter understands, which is that it's difficult for any work that he might be associated with to receive a dispassionate hearing,'' said the official, who spoke to reporters at the Pentagon today on the condition of not being named.