Hi,
As per above, you'll need to ask specific insurers and/or their agents/brokers that you have a US licence. There'll be many insurance companies who won't insure you, but there are quite a number who will.
The actual quote will also depend heavily on the type of car you wish to get insurance on, your postcode etc. When a driver with a non UK full licence applies for insurance, the price is loaded higher due to the greater risk seen by the insurance companies. Bottom line is you'll need to shop around quite a bit to see if you can get an acceptable premium based on all the above.
Cheers, DtM! West London & Slough UK!