I can't complete mission seven harkonnen. They start you out with a couple tanks, quads, trikes, and a unit of light infantry and you are supposed to take over the atredies construction yard.

I take the engineer over, capture the construction yard and begin to build structures and defend the base. However, they send ridiculous amounts of atredies troops from the northeast and purple sardukars from the southeast and kill me every single time. I can't get the defenses strong enough to withstand all those cars and troops. There is just not enough time. I tried rushing, going slow, and even hiding the initial force in another location. They still get me every single time.

How can I compete this mission???? Thanks for your help.

build a wall to block the access up the ramp in the SE.
send 3 engineers north then west to capture the enemy buildings (radar, heavy factory, power)...have a slab ready to build adjacant to the captured buildings so that you can build in the future...they'll waste the buildings quickly. As soon as the slab is in place cash in the buildings.
build gun turret at the southern point, directly below your construction yard...this will get forces moving from the east to attack your west. eventually you'll have about 6 gun & missile turrets there.
build up the west with turrets and walls and play defensive there.
In the captured area, build barracks to produce engineers for capturing enemy buildings (they get taken out quickly at first) and turrets to support them. Taking this area reduces the attacks dramatically.
Save often. You'll reload a lot.
After that it's easy...until you get to level 9

Playing as Atreides, 1st send your infantry all the way to the top left of the screen to destroy the enemy construction yard. If you don't succeed in that you can't win the game. After that, take what few tanks you have and ambush aerial invaders also on the left side of the screen. If you survive, build a double wall around your camp with missile towers. Build Ornithopters and bomb the Harkonnen. Take out the trooper barracks because they can destroy camp walls and win. After that you can mop up any way you like.