The API doesn't provide for submission at this time. You can
encourage your readers to submit Digg stories by adding "Digg This"
buttons to your web site:
http://digg.com/tools/integrate
>Is there any existing API that I can use or any chances of
>developing it in future?
This is a common question, so you'll find several past discussions by
searching the forum:
http://groups.google.com/group/diggapi/search?q=submit
We're working on OAuth to allow tighter integration of activities
like digging, commenting, submitting, and so on. Note that OAuth
isn't a way of automating such activities, but rather allows people
who use Digg to authorize API applications to act on their
behalf. So diggs, comments, and submissions still would come from
people, not directly from applications.