I need to install a door in a load bearing concrete block wall between my garage and utility room. What should be the length, width, and thickness of the lintel plate I install over the rough opening?

How tall is the loading bearing wall and does that wall carry the roof load too? Back to you.

It is a standard 8 foot wall.

Still didn't hear if it carries the roof load but you don't need much if its an 8" wall. Two pieces of 3/16 " angle lintel should do it. Extend into the wall 6" each side of the rough in.

Sorry, I misunderstood your question. The wall in question runs down the center of the house and supports the attic floor joyces. The roof is supported by rafters with center poles running at intervals to the center support wall of the house. The outer ends of the roof rafters are supported by the outer walls.