run with the hare and hunt with the hounds

One cannot run with the hare and hunt with the hounds — на двух стульях не усидишь; за двумя зайцами погонишься, ни одного не поймаешь

run with the hare and hunt with the hounds -- и нашим и вашим

Example: We've had enough of Tony Blair trying to run with the hare and hunt with the hounds. — Нам всем надоело двурушничество Тони Блэра..

Syn.
No man can serve two masters
Between two stools one falls to the ground

see also
[на два фронта]