The agency may appear in an action seeking an award of support on behalf of a child owed a duty of support, or to enforce a spousal support order if a spousal support obligation has been established and if a support obligation, established with respect to a child of that spouse, is also being administered, and may also appear in an action seeking modification of a support order, decree, or judgment already entered. Action under this section may be undertaken upon application of an obligee, or at the agency's own discretion if the obligor is liable to the state under AS 25.27.120(a) or (b).