How to correctly texture terrain?

Actually, what I am trying to achieve is a textured terrain(.obj), and a textureAtlas(.png). I then want to load it into a game. The main problem is that when I tried to texture terrain created in blender, it exported the terrain’s texture. And that is not what I want, it might cause some performance tweaks at a final version, because i will have to bind terrain’s texture for every terrain chunk when rendering. I created a textureAtlas that contains grass texture and rock texture, and I want to texture the terrains using the textures from textureAtlas. So in Java code, I just bind the textureAtlas once and render all terrain chunks.

Is there any way to achieve that in Blender?

-Thanks in advance.

UP

Well, imagine that you created 10 house models, each of them is different and they are in separate meshes. They all use the same textures, so why don’t you make them use the same texture regions(textures in texture atlas)? Thus, they don’t have their own texture and it is much better…

That’s what i want.

Or in other words, make the vertices to use tex coords from 0 - 0,5(if there are 2textures in texture atlas and I want to draw the first region).