Upvote:2
You should always declare the refusals. US and UK shares immigration data and they will know that you has been refused US visa before. So, lying about it in the application is a sure way to get a refusal.
On the other hand, your situation is different for a visit and study and therefore that will be assessed independently. You have a higher chance of getting a student visa, as you have been accepted in a UK school, provided you satisfy other criteria.