Oh, I see you're at 'the room'. If you're weaksauce, try this...
After you kill someone with a single bullet and pick up their dropped ammo, run out the door and reenter. This will reset all the remaining bad guys to their original positions and serve as an autosave.
To recap...
-Bullet to the head/knee, when they're stunned, kick them to the floor and knife them on the ground.
-If they don't drop ammo, restart from save point.
-If they do drop ammo, run out the door to save the game.
-Repeat until you've built up your ammo reserves.
Obviously taking out the 'snipers' with your rifle and getting rid of the guys with shields is your first priority.