“My question is, why? What’s missing and what’s going on?” said a senior Senate aide who had been given a preliminary briefing on the new service.

In some respects, the broad outlines of the plan are reminiscent of Pentagon efforts under Defense Secretary Donald H. Rumsfeld to move the military into areas of intelligence that had long been the domain of the CIA.

But a second congressional official, who also was not authorized to discuss the program publicly, said the coordination behind the new plan, in which the DIA’s program will be more closely modeled on its CIA counterpart, has eased some of those long-standing concerns.

“If this were an attempt of the type we saw during the Rumsfeld years to consolidate human intelligence to have a better bulwark against what the CIA is doing, that would be a concern,” the second congressional official said. “But I don’t think that’s what's going on.”

The plan was unveiled about a week after a senior U.S. Army officer with extensive experience in Special Operations and counter­insurgency fighting in Iraq and Afghanistan was nominated to serve as the next chief of the DIA.

While serving in Afghanistan, Lt. Gen. Michael T. Flynn published a harsh critique of intelligence operations in that country, criticizing collectors as being too focused on tactical threats and failing to understand the broader demographic and political context of the battlefield.

About 15 percent of the DIA’s case officers will be part of the Defense Clandestine Service, the defense official said. New, more clearly delineated career paths will give DIA case officers better opportunities to continue their espionage assignments abroad, he said.

The new service fits into a broader convergence trend. U.S. Special Operations forces are increasingly engaged in intelligence collection overseas and have collaborated with the CIA on missions including the raid on Osama bin Laden’s compound in Pakistan and ongoing drone strikes in Yemen.

The blurring is also evident in the organizations’ upper ranks. Panetta previously served as CIA director, and that post is currently held by retired four-star Army Gen. David H. Petraeus.