ATF is for an automatic transmission. Automatic Transmission Fluid. If you're talking about putting Power Steering fluid in the transmission, I'd say no you can't. If for some reason this automobile requires ATF in the power steering equipment, I'd also say you can't use power steering fluid. They're quite different in terms of the additives. For the 99 Legacy the manual refers to using Dextron II, III or other. That's GM stuff. You can't use Ford ATF. I would check your manual which will tell you what you can use. Power Steering Fluid and ATF are generally one in the same. The additive issue probably is more important for the Tranny than the Pwr Steering pump. Some people mix the ATF up with brake fluid which will cause MAJOR problems.
The 2004 Subaru Impreza runs on regular unleaded.
The 2003 Subaru Impreza runs on regular unleaded.
The 2014 Subaru Impreza runs on regular unleaded.
The 2008 Subaru Impreza runs on regular unleaded.
The 2001 Subaru Impreza runs on regular unleaded.
The 2010 Subaru Impreza runs on regular unleaded.
The 2009 Subaru Impreza runs on regular unleaded.
The 2013 Subaru Impreza runs on regular unleaded.
The 2002 Subaru Impreza runs on regular unleaded.
The 2012 Subaru Impreza runs on regular unleaded.
The 2005 Subaru Impreza runs on regular unleaded.
The 2011 Subaru Impreza runs on regular unleaded.