Malta to FCO to Dulles

From the KM Malta website: If you have booked your connecting flights together, i.e. you have one booking reference with the same ticket number including both/all flight sectors, you can check-in yourself and your bags at once. This allows you to skip checking in again at your connecting airport.

So the answer would appear to be yes. Just make sure by checking the airport identifier when they tag your bags.

The answer SHOULD be yes, at least in theory (no guarantees).

According to ExpertFlyer (an excellent and vast resource for arcane details about most airline flights), yes, KM Malta Airlines (airline code: KM) can indeed "interline" and transfer checked baggage to United Airlines (and a couple hundred others). Now, it's always possible you could run into a technical issue or a surly/poorly-trained agent, but their system should be set up to allow that interline bag transfer. Keep your fingers crossed and be ready to intervene if needed, but with any luck it should go smoothly.

(Disclaimer: I have no direct, personal experience interlining baggage between these two airlines. I have  been to Malta, and I have  had baggage transferred seamlessly between United and other airlines many times, and I do trust the info pulled from ExpertFlyer. But nothing in this world is perfect. Except perhaps that pizza I had on Gozo last year, that was about as close to perfection as pizzas get.)

Thanks for your replies!

I confirmed with KM Malta. My flights are under one ticket number and they have an agreement with United, my bags will be booked through to IAD.