Mr. Obama notably did not commit himself to providing arms to the rebels he is recognizing or to supporting them militarily with airstrikes or the establishment of a no-fly zone, a stance that has led to a rise of anti-American sentiment among many of the rebels.

The United States has played an active role behind the scenes in shaping the opposition, insisting that it be broadened and made more inclusive. But until Mr. Obama's announcement on Tuesday, the United States had held off on formally recognizing the opposition coalition, asserting that it wanted to use the lure of recognition to encourage the rebel leaders to flesh out their political structure and fill important posts.

In recent weeks, the National Coalition of Syrian Revolutionary and Opposition Forces has been in the process of developing a series of committees on humanitarian assistance, education, health, judicial matters and security issues.

Mr. Obama’s statement was an acknowledgment that the opposition had made sufficient progress to merit recognition. The American hope is that the opposition, in conjunction with local councils that are being formed in Syria, could help govern areas that have been wrested from Mr. Assad's control, provide public services like law enforcement and utilities, and perhaps even channel humanitarian assistance. Alluding to this role, Mr. Obama said that the opposition would “have some responsibilities to carry out.”

But Mr. Obama's move does not go so far as to confer on the opposition the legal authority of a state. It does not, for example, recognize the opposition's right to gain access to Syrian government money, take over the Syrian Embassy in Washington or enter into binding diplomatic commitments.

It is also unclear to what extent the move might influence the situation inside Syria, where the pace of the fighting appears to have intensified. A senior American official who is attending the meeting in Morocco said on Tuesday that none of the rebel military commanders from the Free Syrian Army would be attending the meeting on Wednesday.

“There are people here who definitely coordinate with armed groups, with the Free Syrian Army,” he said. “That is not to say they are giving instructions to it; they do not. It is not to say that they are telling it what to do or what to say in the international field; they are not. In a sense, the Free Syrian Army is a separate organization.”

Andrew J. Tabler, a senior fellow and a Syria expert at the Washington Institute for Near East Policy, said: “The recognition is designed as a political shot in the arm for the opposition. But it’s happening in the context of resentment among the Syrian opposition, especially armed elements, of the White House’s lack of assistance during the Syrian people’s hour of need. This is especially true among armed groups.”