WASHINGTON  Representative John P. Murtha, chairman of the House military spending subcommittee and a decorated former Marine, has long acted as a protective Uncle Jack to the Marine Corps.

Now the corps has named one of his nephews, Col. Brian Murtha, to the office charged with advocating for its interests on Capitol Hill, where Representative Murtha, Democrat of Pennsylvania, helps write the military budget. In relocating to be near the Pentagon, Colonel Murtha has even moved into a unit in the same condominium building where his influential uncle lives in Arlington, Va.

This convergence of the Murthas is an example of Washington’s special centrifugal force that so often brings relatives together on opposite sides of the same table. It does not appear to violate any rules or ethics guidelines, though it may well raise some eyebrows among legislative liaisons competing for resources on behalf of the other military services.

“I am sure that he provides a valuable service to the Marines,” Lt. Col. Christopher Garver, an Army spokesman, said of Colonel Murtha, declining to comment further.