At times, the politically progressive leaders of some of the organizations — many from the Vietnam era — take positions that appear out of step with more socially conservative members from previous wars. This has irritated Robert L. Wilkie, the Veterans Affairs secretary, who views these as unwelcome partisan positions, said several agency and veterans’ group officials.

Last April, Mr. Wilkie hosted a breakfast for veterans’ service organizations that included representatives not just of the traditional Big Six, but also the Independence Fund and Concerned Veterans for America, which is financed by Charles G. and David H. Koch, who have backed conservative causes.

The Koch-supported group was instrumental in ousting the last head of the department. It has also been pushing for more health care to take place outside the V.A. system, with the first step beginning soon under a sweeping new law. Their voices were welcomed by House Republicans as they passed the measure this year.

At a hearing last month on Capitol Hill, some Democrats suggested that Mr. Wilkie was ignoring the opinions of traditional organizations on this law. “A lot of V.S.O.s have talked to me about the communication within the V.A.,” said Senator Jon Tester of Montana, the ranking Democrat on the Senate veteran committee. “It’s not where it needs to be.”

Mr. Wilkie made his position clear. “Half of our veterans are now under the age of 65,” he said, “which means they have different cares, they have different interests. What I have done in my short time is actually open the aperture to the table at the Department of Veterans Affairs to bring in veterans who are not traditionally part of the system.”

The shifts, while perhaps inevitable, leave some worrying that the hard work of pressing for the complicated and expensive health care needs, and other issues, will lack a generation of new leaders.