I have a 1997 Outback and I've been having some issues with the factory (dealer installed) alarm.
Assuming your's is like mine, there should be a little bypass button under the driver's side dashboard, behind the hood release lever. I had to crawl around to find mine the first couple of times - unfortunately I know where it is all too well now.
So, when you find the button, which is a bit smaller than a pencil eraser, put your key in the ignition and turn it to the ON position. Press and release the bypass button. That should disarm the alarm and let you crank the car. You may have to hold the button while cranking the car.
There are two 20 amp fuses on my alarm, which is a small flat black box that hangs on wire ties in the same general area under the dash as the bypass button. If you remove the fuses, the car will crank and the alarm will be disabled. I was tempted to do that permanently but your key fobs probably won't work if you disable the alarm.
Mine seems to act up in cold weather, making me wonder if snow and ice are building up on a shock sensor somewhere. Who knows?
Source: Subaru security system operator's manual INS0754 revision A