If you mean that the transformer's secondary is rated for 1A and you want to use a 3A fuse in series with it, there's a fair chance that if there's a fault downstream of the secondary (e.g. a shorted rectifier), the transformer won't be able to supply enough current to blow the fuse. So I would say no, don't do it. Use a fuse around 1.5A. Also, use a slow blow fuse, so it won't blow on the surge when the smoothing capacitor(s) charge up when power is switched on.