WASHINGTON  The Justice Department has concluded that the Obama administration can lawfully pay the community group Acorn for services provided under contracts signed before Congress banned the government from providing money to the group.

The department’s conclusion, laid out in a recently disclosed five-page memorandum from David Barron, the acting assistant attorney general for the Office of Legal Counsel, adds a new wrinkle to a sharp political debate over the antipoverty group’s activities and recent efforts to distance the government from it.

Since 1994, Acorn, which stands for the Association of Community Organizations for Reform Now, has received about $53 million in federal aid, much of it grants from the Department of Housing and Urban Development for providing various services related to affordable housing.

But the group has become a prime target for conservative critics, and on Oct. 1, President Obama signed into law a spending bill that included a provision that said no taxpayer money  including money authorized by previous legislation  could be “provided to” the group or its affiliates.