WASHINGTON — The Department of Veterans Affairs is preparing to shift billions of dollars from government-run veterans’ hospitals to private health care providers, setting the stage for the biggest transformation of the veterans’ medical system in a generation.

Under proposed guidelines, it would be easier for veterans to receive care in privately run hospitals and have the government pay for it. Veterans would also be allowed access to a system of proposed walk-in clinics, which would serve as a bridge between V.A. emergency rooms and private providers, and would require co-pays for treatment.

Veterans’ hospitals, which treat seven million patients annually, have struggled to see patients on time in recent years, hit by a double crush of returning Iraq and Afghanistan veterans and aging Vietnam veterans. A scandal over hidden waiting lists in 2014 sent Congress searching for fixes, and in the years since, Republicans have pushed to send veterans to the private sector, while Democrats have favored increasing the number of doctors in the V.A.

If put into effect, the proposed rules — many of whose details remain unclear as they are negotiated within the Trump administration — would be a win for the once-obscure Concerned Veterans for America, an advocacy group funded by the network founded by the billionaire industrialists Charles G. and David H. Koch, which has long championed increasing the use of private sector health care for veterans.