Is it doable: yes. Would I take the risk: no. The average delay of FCO-CDG flights is around 20min. Which means that your probability of arriving more than 30min late is significant. AF staff might be waiting to help you, but there is extra security to get on a US flight (assuming that they have checked all your documents at FCO).
AF sells FCO-LAX with a 1 hour connection on the early flights, but that is because there are 3 flights to LAX, so you can be rerouted on a later flight if the FCO-CDG leg is delayed. However, I personally would not take the risk of a short connection if you are transferring to the last CDG-LAX flight of the day.