But the decision, made at the White House a week ago, goes considerably beyond that.

While the administration said it would continue to try to persuade companies like Apple and Google to assist in criminal and national security investigations, it determined that the government should not force them to breach the security of their products. In essence, investigators will have to hope they find other ways to get what they need, from data stored in the cloud in unencrypted form or transmitted over phone lines, which are covered by a law that affects telecommunications providers but not the technology giants.

Mr. Comey had expressed alarm a year ago after Apple introduced an operating system that encrypted virtually everything contained in an iPhone. What frustrated him was that Apple had designed the system to ensure that the company never held on to the keys, putting them entirely in the hands of users through the codes or fingerprints they use to get into their phones. As a result, if Apple is handed a court order for data — until recently, it received hundreds every year — it could not open the coded information.

Mr. Comey compared that system to the creation of a door no law officers could enter, or a car trunk they could not unlock. His concern about what the F.B.I. calls the “going dark” problem received support from the director of the National Security Agency and other intelligence officials.

But after a year of study and extensive White House debate, President Obama and his advisers have reached a broad conclusion that an effort to compel the companies to give the government access would fail, both politically and technologically.

“This looks promising, but there’s still going to be tremendous pressure from law enforcement,” said Peter G. Neumann, one of the nation’s leading computer scientists and a co-author of a paper that examined the government’s proposal for special access. “The N.S.A. is capable of dealing with the cryptography for now, but law enforcement is going to have real difficulty with this. This is never a done deal.”