Banks are trying to unload loans once thought to be the safest form of energy credit. Debt backed by oil and gas reserves are being offered at discounts as increased scrutiny by regulators and investors has forced lenders to set aside more cash to cover losses, the law firm Haynes & Boone LLP said in a note to be delivered to clients Monday. Some banks that bought slices of syndicated loans may try to sell their entire portfolio, according to the note. Reserves-based lending was long considered safe because banks historically got back every penny they lent, even after default, according to a 2013 Standard & Poor’s report. Moody’s Investors Service Inc. said in an April 7 report that lenders could lose 21 cents on the dollar on defaulted exploration and production loans, four times more than the historical average.