I was wondering if anyone knew if someone who resides in the US but is not a citizen or permanent resident (for example an international student) can buy and sell stocks online (using sites like scottrade or etrade) in the US? I do have a social security number and I am also authorized to work but I am not a citizen or permanent resident.

Buy and Sell stocks now a days nothing but gambling. Keep in fixed deposits without any panin and evergreen. You will loose nothing. Mutual funds are also depend up on the market conditions only.