WASHINGTON  A case that began four years ago with the tantalizing and volatile premise that officials of a major pro-Israel lobbying organization were illegally trafficking in sensitive national security information collapsed on Friday as prosecutors asked that all charges be withdrawn.

From the beginning, the case against the lobbyists for the American Israel Public Affairs Committee was highly unusual. The two, Steven J. Rosen and Keith Weissman, were charged under the World War I-era Espionage Act, accused of improperly providing to their colleagues, journalists and Israeli diplomats sensitive information they had acquired by speaking with American policy makers.

Some lawyers at the Justice Department had always had significant reservations about the case, some current and former officials said. They believed that Mr. Rosen and Mr. Weissman had acted imprudently, but doubted that either man should be criminally prosecuted. Nevertheless, F.B.I. agents poured substantial resources into the case, and the decision to seek a dismissal infuriated many within the law enforcement agency.

But several current and former officials said the decision to abandon the case was no surprise. With adverse judicial rulings making the prosecution increasingly risky, lawyers in the United States Attorney’s Office in Alexandria, Va., and at Justice Department headquarters met on several occasions in recent weeks, agonizing over whether to go forward with the trial, which was scheduled to begin June 2.