WASHINGTON — Just a month before a peace conference that will seek an end to the grinding civil war in Syria, the Obama administration’s decision to suspend the delivery of nonlethal aid to the moderate opposition demonstrated again the frustrations of trying to cultivate a viable alternative to President Bashar al-Assad.

The administration acted after warehouses of American-supplied equipment were seized Friday by the Islamic Front, a coalition of Islamist fighters who have broken with the moderate, American-backed opposition, but who also battle Al Qaeda.

Administration officials said that the suspension, confirmed on Wednesday, was temporary and that the nonlethal aid, which is supplied by the State Department, could flow again.

But with rebels feuding with one another instead of concentrating on fighting Mr. Assad, and with the United States still groping for a reliable partner in Syria, the odds of any peace conference breaking the cycle of bloodshed appeared to have dimmed. For the White House, which has pinned its hopes on a political solution, the fracturing of the opposition raises a number of thorny questions, including whether the United States should work more closely with Islamist forces.