Check 'værnsfælles' on http://iate.europa.eu/iatediff/SearchByQueryEdit.do

You will not find a single word in English, so you will have to rephrase it to fit your context, but it means authorities with command over all the defence services.

You might be able to use inter-service, but this is tricky, as shown in this extract, which uses it in two slightly different senses:

The collapse of the Soviet Union revealed that the US had overestimated its military strength. The Pentagon developed a vested interest in exaggerating it. **Inter-service rivalries,** particularly between US Navy and US Airforce, resulted in an arms race between them. The MoD from time to time plants stories about Pakistan's growing military power. Most are self-serving. We cannot allow an uncontrolled nuclear arms race by fuelling raw passions. The military can be very good at this and we must guard against it.

Since nuclear weapons are not war fighting-weapons the traditional military must not have them. **A separate inter-service command** under full and direct civilian and political control must be evolved.

http://www.expressindia.com/news/ie/daily/19980605/15650044....