The US authorities have no direct access to the files of the Criminal Records Bureau. They would only know about a police caution if it was included as part of the information passed on by the British security services. (e.g. if someone is suspected of having links with a terrorist organisation, the UK authorities would probably pass on every bit of information that they had about that individual, including any cautions. However, 'routine' police cautions are not notified to the US authorities).
A caution is not a conviction so, if you're simply asked whether you've ever been convicted of an offence, you don't have to mention the caution.
However, the US embassy website states that you're required to declare any arrests (even if you were totally innocent). So, if you were arrested for the incident which led to the caution, you're meant to declare this. Once again though, the US authorities wouldn't normally know about any arrests.
You've not said why you're required to attend an interview for a visa. If it's because of a conviction or an arrest, which you've already declared (or are going to), you should be aware that the US embassy requires you to obtain a copy of your police record and take it with you to the interview. If so, you should check to see whether it mentions the caution, as it would obviously be foolish to deny something which was already in writing.
Chris