If I have found account activity that might be indicative of fraud, can I discuss this with federal law enforcement? If so, can I discuss the issue freely?

What type of activity? Can you discuss within your Bank's channels first?

That has been done. It is possible fraudulent activity. Am I prohibitied from discussing with federal law enforcement?

The right way to handle a case like this used to be to file a SAR and let them come to you with a subpoena. RFPA otherwise prohibited disclosure of customer info to federal agents.

If the fraud is committed against the bank, and the bank is the victim, there is no reason you can't discuss the issue with LE. You have the right to seek redress for any crime committed against the bank (i.e. a bank robbery), and there is no expectation of privacy when one commits a crime against someone even if it is a financial institution. However, if the fraud is committed against another party, then you should follow the suggestions given regarding filing a SAR.

Actually, you need to file a SAR, assuming the dollar thresholds are crossed, regardless of whose ox is being gored by the fraud. The difference is that you can certainly talk to LE before filing, for all the reasons West Coast Comp listed, if the bank is the victim.