Your agency wants the contract. Your agency wants to and receives the vast majority of funding from the American tax payers. Thus, your agency is not allowed to discriminate. Pretty simple.
Well it's simple except that in order to adopt out children to "gay marriages" the church would be condemning itself to obliteration, and thereby be forced to abandon its freedom to practice its core faith values. Read Jude 1 of Jesus's NEW Testament when you get a chance.
Requiring someone to violate their religious freedom cannot be a secular law. So I don't think it's going to be as simple as all that. What you're up to is forcing churches and faithful people to disgorge their protected orphans into the clutches of lewd sex street performers and their 100% -supportive sychophants/sex cult.
I think this is as they say..."where the rubber will meet the road" on the gay marriage debate in the courts... There is something "simple" about it though in the end.. The choice will be one the judges will have to make about what is more important:
1. Children or
2. The cult of LGBT who wants to force churches to surrender kids to them.