I am going to pour a slab in a pole barn. I want to have 4' high by 12' long concrete wall on both sides of the wash bay. Can I form the walls up so that I can pour the walls and the slab at the same time?

Usually not since the wall forms need to sit on the floor for support. It can and has been done just like pouring a concrete stair stoop. It may not be saving you time like you think and it certainly is not going have a significant savings with materials.

THe problem is that concrete is $98.oo a yard and if I order less the 4 yards they charge another $50.00 to deliver. THe walls will only take a little over a yard.

It can be done but unless you are very familiar with forms and concrete it will be difficult to get a good job. Maybe this would work for you, when you pour the concrete for the slab install a row of re-bar in the center line of the two walls, let the re-bar stick above the concrete slab 4" or so. After the slab is cured lay a row of concrete blocks letting the re-bar stick up into the cavities in the blacks. Fill the cavities in the blocks with concrete, it shouldn't take much so it can be mixed from the bags of pre mix from HD.