Michael Allen, a national security aide in the Bush administration who also worked for the House Intelligence Committee, said that if nothing else, the changes may inspire confusion and risk aversion. Referring to the bulk data collection, Mr. Allen said, “The president says it is important, could have helped us prevent 9/11, it has worked, there are no instances of abuse, but we should change it anyway.”

The bulk data program seemed to cause the most difficulty for the president as he pondered what to do about it. His review panel suggested taking the data out of the N.S.A.'s hands and leaving it with telecommunications companies or a newly created independent entity. The N.S.A. could then tap it only in certain instances while investigating terrorist links.

Mr. Obama deemed both of those ideas unworkable and so put off a decision by saying he supported the goal of removing the data from the N.S.A. but would ask Attorney General Eric H. Holder Jr. and James Clapper Jr., the director of national intelligence, to come up with a way of doing that. He also sought ideas from Congress, which would have to pass legislation to change the program.

In the meantime, he set out a new rule that “the database can be queried” only with permission from the surveillance court, but allowed an exception “in the case of a true emergency.” He did not define what would constitute such an emergency or who would determine whether a situation qualified. Nor did he clarify whether the court would have to approve each time a new telephone number was searched or each time a new target was searched. But some program supporters expressed concern that it could take too long.

He also limited the scope of searches, allowing analysts to study data two layers removed from the target, instead of three. Intelligence officials have accepted such a change because the amount of data expands so vastly three layers out that it becomes less useful.

The details matter, and may become clearer in coming days. But for a president who came to office promising to end what he considered the excesses of the new security state, Mr. Obama’s speech on Friday was as much about the larger question of faith. Rather than throw out the programs at issue, he hoped to convince the public that they are being run appropriately.