Some real estate agents have started raising red flags.

“When you decide to sell your house you may find it difficult to do so because many banks, here and elsewhere, will not mortgage properties with gas leases, which, in turn, limits the number of buyers willing and able to buy your property,” wrote Linda Hirvonen, an agent in Ithaca, N.Y., in a newsletter last month.

Banks establish rules for how mortgaged properties can be used, to help ensure that they will hold their value. Banks also need to guarantee that their mortgages meet certain standards so that they can sell them to institutions like Fannie Mae and Freddie Mac, which bundle and sell these mortgages to investors.

“In terms of litigation, there is a real potential for a domino effect here if lenders at each step of the way made guarantees that are invalid,” said Greg May, vice president of residential mortgage lending at Tompkins Trust Company, headquartered in Ithaca.

Banks resell more than 90 percent of new residential mortgages in the United States to institutions like Fannie Mae, Freddie Mac and Ginnie Mae. It is not clear how many mortgages held by major secondary lenders or investors have oil or gas leases on them that do not comply with mortgage rules.

But if even a small percentage do, tens of billions of dollars in mortgages might be affected, raising new concerns for an industry that has suffered in recent years from home loans that proved much riskier than expected.

Some lawyers who specialize in oil and gas leases said they were not worried.

“The leases have not created any practical conflict or issue with mortgages,” said Adam J. Schultz, a lawyer in Syracuse, adding that there are thousands of gas leases on mortgaged properties in New York and Pennsylvania and that state environmental regulations helped protect property values.

Most of the bankers and mortgage experts interviewed also emphasized that they were not opposed to expanded drilling. The surge in such drilling has created thousands of jobs, bolstered American energy supplies and turned some landowners into millionaires, they said.