It not been said but the handmaids are slaves right

Well, all of them are slaves, really - the handmaids, the Marthas, the Jezebels, the unwomen sent to the colonies.

Even the wives have rooms in their own houses that they aren't allowed to enter, have to watch their husband f*ck a handmaid all the time, are obligated to all wear the same color, and the only way they can take a stroll outside is with a Guardian attached.

I would agree that most of the people in Gilead are slaves of the state. They are not the property of any particular individuals, but rather are assigned to serve the various commanders by the state.

Even Nick, a driver, soldier, spy, guard has very little freedom. He lives with his commander, had no personal life and was assigned a wife. What would have happened to him if he refused his child bride?

In effect, their status is little better than slavery, but I guess technically slavery involves the classification of a living human being as chattel property, thus not as human beings. I think all persons in the plot are treated as human beings, however, the issue is that we are dealing with a theocracy, and a highly dictatorial one at that. So essentially everyone's freedoms are extremely limited (some more than others), as everyone must live according to the dictates of what the leaders consider God's commands.

They are worse off than slaves were in the past. I read that Offred (or the author) even said that Handmaids were just seen as a uterus with legs (which is actually how many sand rats view women in the Middle East). Even in ancient times, slaves (even female ones) could have their own names and be allowed to do things these Handmaids are not.