You´ve got two problems and not one.

1.:clip_far is the value that clips your level in the distance.
Just set it to a higher value.

2.:clip_near is the value that clips all the faces close to your
camera and defines the resolution of the z-buffer.
Setting it to a higher value it will remove the flickering in the distance
that apears on small blocks borders. But it will also clip the faces near to
your camera. So you have to change the value dynamicly depending of the distance
levelgeometrie has to your camera.

The only problem left is if you´re in a position where you have faces close to
the camera but you can look into the far distance too.
I haven´t deeply thought about that problem now, but maybe you find a solution.
It would be absolutely kind of you to publicate it then.

cu
Lutz