You must keep your passport valid at all times while you are in the U.S. (unless you are exempt from passport requirements).
If your passport will expire while you are still in the U.S., you must contact the embassy or consulate of your home country in order to make arrangments to have your passport extended. You will not be permitted to re-enter the U.S. with an expired passport. If you lose your passport, you should immediately take steps to have it replaced. Please contact the OISS for help.