In addition, the officials said, the council simply lacks the ability to navigate the tangled logistics of getting aid such as flour, blankets and food into an active war zone.

As it stands, many international aid agencies are following a two-track system, distributing aid through official channels in Damascus – for which they are criticized by some opposition figures – but also through independent, cross-border pipelines, trucking it in through Jordan and Turkey to opposition-controlled areas inside Syria. A third cross-border aid pipeline, via the northern Kurdish region in Iraq, is expected to open soon, the executives said.

The State Department appears loath to change that delivery process, which took no small amount of diplomacy to set up with contacts on the ground in Syria, as well as the governments in Ankara and Amman. Beside, U.S. officials have said, distributing aid via a shadow, unrecognized governing body would be virtually unprecedented; most everywhere else, U.S. assistance is doled out via the United Nations or partner nongovernmental organizations.

Anne Richard, assistant secretary of state for population, refugees and migration, made it clear in a recent phone call with journalists that while the Syrian opposition council is valuable in providing contacts and assessing what places need aid, there were no plans to use it as a delivery mechanism.

“Aid is supposed to be delivered not based on one’s political beliefs or which side one’s picking in a war or which faction one belongs to, but instead based on need,” Richard said. “So their assessment, their networks are very important to us, so we want to work with them. But right now, they’re not built as an organization to deliver aid.”

McCain and other members of the congressional delegation that met with the opposition leadership are more confident that the council is up to the task, pointing out that the council has now established a wing that focuses on aid.

“Having built an assistance component of the council, we strongly believe that it is time to empower the council to deliver humanitarian aid with sufficient vetting to ensure aid reaches the people of Syria,” the delegation wrote.

But the humanitarian aid executives said the opposition’s “assistance component” is just two people. They point out that their own agencies are still struggling to meet demand even with large staffs, longstanding ties to U.S. government agencies and operations in Syria and several of its neighbors.

What McCain and the others really want to do, the aid executives said, is to “stand up a Syrian opposition through humanitarian aid.” They noted that the coalition is already receiving $50 million in State Department funds to turn itself into a legitimate, credible government in waiting that’s poised to take charge should Assad’s regime crumble.

“I don’t think it’s a question of the administration not helping the Syrian opposition,” one of the humanitarian officials said. “But we would draw a line with the senators’ conclusion that all aid or most aid needs to be funneled now through the Syrian opposition, where there’s just no capacity to provide that.”

The dispute over humanitarian aid comes as the Obama administration also is being criticized for refusing to provide military aid to the opposition. President Barack Obama vetoed a proposal for military assistance to the rebels that had the backing of four senior advisers, including Hillary Clinton, then the secretary of state, retired Army Gen. David Petraeus, then the CIA director, and Defense Secretary Leon Panetta.

The White House explained that rejection last week by saying lethal aid to the rebels would endanger the Syrian people, Israel and the United States – an apparent reference to the al Qaida-affiliated Nusra Front, a rebel faction that has become its leading military arm but that was added to the State Department’s list of international terrorist groups in December.

New Secretary of State John Kerry has indicated that stance isn’t softening, voicing concern on several recent occasions over the involvement of the Nusra Front in the rebel movement.

The opposition coalition’s president, Sheik Mouaz Khatib, has criticized the State Department’s designation of Nusra as a terrorist organization.