Yes, you can sue. No, you won't win.
Employers aren't REQUIRED to offer 401k benefits to ANY employee at all. Moreover, even if they offer it, it might be opt-in -- meaning, you have to enroll in the program. There's nothing illegal about this. It might have even been laid out in the employee handbook (where you got the "information" you say led you to ask this question).
Also, from a pragmatic perspective, litigation is always expensive, and suing your employer as a first-strike option is a particularly bad idea in most circumstances. There's lots of intermediate steps (including, say, talking to HR or your boss?) that don't even require a lawyer, and some steps in between that COULD involve a lawyer but don't involve litigation. Frankly, there's also perceptual and interpersonal problems that you could create by suing your employer that may not, on balance, be worth the expected gains. (here, possibly $0).
I'd advise you if you're serious about this to call a MO employment lawyer who offers a free consultation and talk to them; they might have different advice for you than I do, but I suspect they'll tell you the same thing.
Good luck, though.
Answers to legal questions are usually fact-dependent; my answers are general and based on the facts as you describe them and necessarily includes assumptions. More specific answers can be provided only after researching the appropriate law and a comprehensive consultation in which all relevant facts are disclosed. Until both a retainer agreement is executed and we have a consultation, I am not your lawyer and you are not my client. Moreover, I cannot be your attorney unless you are located in Missouri, the only state in which I am licensed. If you are not in Missouri, please consult an attorney in your state for assistance, as my advice may be incorrect or incomplete. This uncompensated answer is provided for informational purposes only, as a free public service; any reliance thereupon is at your sole risk.