WASHINGTON - The Islamist consolidation of power over Syria's rebel movement in recent weeks is another indication that foreign policy strategists are correct when they warn that the Syrian conflict is likely to grind on for years before either side is prepared for serious peace negotiations.

Despite the staggering death toll and worsening humanitarian crisis, experts say, the conflict isn't yet "ripe" - a term professional mediators use for the point when warring parties recognize that both sides are suffering from a stalemate and are ready to find a mutually acceptable settlement. That phase is a long way off in Syria, analysts say, and the collapse of the moderate rebel command underlines why next month's peace summit in Geneva is considered an exercise in futility.

Holding the conference at this juncture presents a difficult choice for the United States, which is struggling to find Syrian opposition partners who can form a credible, representative delegation to sit across the table from the more sure-footed, fully supported representatives of President Bashar al-Assad's regime.

The biggest challenge now is how to have a rebel voice in the room, when the Western-backed Supreme Military Council is in tatters and its Islamist rivals reject the Geneva process outright.

Helping to craft an acceptable guest list was always a tough project for the United States; the conference has been delayed repeatedly in large part because of the opposition's disarray. The problem became starker over the weekend, however, when Islamist forces descended on a town along the Turkish border and seized the headquarters and warehouses belonging to the Supreme Military Council, led by the U.S. point man, Gen. Salim Idriss.

Initial accounts, repeated by U.S. officials, said that members of the Islamic Front, a Saudi-backed consortium of six Islamist groups, overran the facilities where U.S.-provided nonlethal supplies were kept. The Obama administration, which has long worried that its aid would fall into the hands of radicals, was alarmed enough to suspend the $260 million rebel aid program. Great Britain followed suit by freezing its own shipments.

The move signaled to close observers of the conflict that the Obama administration finally had recognized how very little clout its Syrian allies had against the ascendant Islamists despite Supreme Military Council claims to represent tens of thousands of fighters. Analysts weren't buying the State Department's insistence that the aid suspension was no indication that the U.S. was easing off its support for Idriss and his men.

On Thursday, the political arm of the U.S.-backed opposition, the Syrian Opposition Coalition, tried to put a bright face on the Islamist fighters' capture of the headquarters, saying they really had come at Idriss' request to fight off an attack by the al-Qaeda-affiliated Islamic State of Iraq and Syria.

But that account was greeted with skepticism.