GMAC Mortgage, one of the country’s largest and most troubled home lenders, said on Monday that it was imposing a moratorium on many of its foreclosures as it tried to ensure they were done correctly.

The lender, which specialized in subprime loans during the boom, when it was owned by General Motors, declined in an e-mail to specify how many loans would be affected or the “potential issue” it had identified with them.

GMAC said the suspension might be a few weeks or might last until the end of the year.

States where the moratorium is being carried out include New York, Connecticut, New Jersey, Illinois, Florida and 18 others, mostly on the East Coast and in the Midwest. All of the affected states are so-called judicial foreclosure states, where courts control the interactions of defaulting homeowners and their lenders.

Since the real estate collapse began, lawyers for homeowners have sparred with lenders in those states. The lawyers say that in many cases, the lenders are not in possession of the original promissory note, which is necessary for a foreclosure.