The route to legally working in the US for non-citizens here on student visas can be difficult, time-consuming, and irritating - however, actuarial science falls under the category of 'specialized' work (work that requires a Bachelor's degree or higher), and applicants can pursue an H1-B Visa, if they get company sponsorship.
After you have a work Visa while employed by a company, you can stay in the country for six years (you have to be working the entire time, and while you can switch companies, your new company has to formally file for your status to transfer), and apply for a green card (again with company sponsorship).
Finally, you can attempt to become a naturalized US citizen, with all of the legal protections citizenship provides. Legally, you would be no different than someone born a citizen.
More on green cards:
http://uscis.gov/graphics/services/residency/index.htm
http://uscis.gov/graphics/services/residency/employment.htm
I can't stress enough that you need to do your homework, understand the process towards legal employment in the United States, and be up front with employers about your need. Not many Actuarial employers sponsor foreign workers, but the better your qualifications and understanding of the process, the better your chances.
Here is a seven year-old list of companies willing to sponsor foreign students. Just remember that whether a citizen or not, you need to send out as many applications as possible, with good cover letters and résumés. Good luck!