Is it permissible to adopt a child or an infant from an orphanage and raise him as a Muslim in America, knowing that adoption is forbidden?

Allah the Almighty has not forbidden anything to His servants except that its harms outweigh and exceed any benefits it may contain. Among these is adoption, for it leads to the loss and mixing of lineages and the prohibition of what is lawful. There is no compelling necessity that calls for its permissibility. The good mentioned by the questioner can be achieved through what the Lawgiver has urged us to do, namely, sponsoring orphans, and even sponsoring foundlings themselves. What is forbidden is adoption in the sense of attributing a child to other than his father, not sponsorship.