I am trying to find a collection of science fiction short stories and artwork which was in my elementary school library back in the early 1980's, however it may have been published in the late 1970's. The stories I remember are:

1. A space battle where soldiers drop from orbit, play dead on a tank and use it to break into an enemy stronghold.
2. Two children who escape an underground city to find giant robots launching missiles into the desert so humans think war is still occurring.
3. A survey team helping a primitive tribe destroy nests of "zwargs" or "Zargs".

There were a couple more stories but those are what I remember. It was a hardbound book with a yellow cover with science fiction artwork. The stories also had various science fiction illustrations.