It should be pointed out that none of the original texts had any punctuation or spaces between the words. Writing was expensive, and space was at a premium. Translators determined the spaces and added the commas and periods during their translations; there are differences among them. Exactly when that occurred with the verses under consideration is unknown.
In Matthew 6:12, the King James Version reads: "And forgive our debts, as we forgive our debtors." Modern versions (New International, Revised Standard) read: "And forgive us our debts, as we also have forgiven our debtors." The differences can be attributed to the fact that there are two different groups of ancient manuscripts, and they fall into those two basic camps. When we pray the words written in the present, we are asking, "Forgive us as is our practice to forgive." When we pray the words written in the perfect, we are asking, "Forgive us as we have, in fact, forgiven." The big problem really lies with the "as." It expresses similarity or proportion. It can mean forgive us in the same way or forgive us in proportion as we forgive others. In either case, this suggests a very close relationship between the divine and human realms of forgiveness. He who is unforgiving cuts himself off from forgiveness.
Now this works in two ways. It includes the one who is unforgiving and is the injured party as well as the one who is unforgiving and has done the injuring. Neither one can be forgiven until they have forgiven.
Translations for Luke 11:4 generally read: "And forgive us our sins, for we also forgive everyone indebted to us." Most scholars accept that "sins" and "debts" are being used interchangeably. "Everyone" is emphatic, meaning that everyone is included. The troubling word here is "for." It also suggests a condition necessary for receiving forgiveness. This is more than simply having a receptive attitude. It requires that we are ready to forgive others. Basically, we have to be willing to give what we have received. God's grace is freely given; yet it demands of us that we be active participants (i.e. doers) and not just takers. The idea is one of imitation. God freely forgives our many sins/debts. Because we have that assurance, we, in turn, are able to forgive those who have wronged us. By making the prayer request we are, essentially, agreeing to the terms.
If we think about this, there is an unexpected expectation or twist in this petition. In a very real sense, we are judging ourselves every time we pray this prayer. The one who chooses not to forgive had best not pray this. We are asking God to treat us as we are treating or have treated others. It puts a whole new face on the power of prayer.