WASHINGTON — The Bush administration warned landowners along the southern border Friday that it will seize their property if they refuse to cooperate with federal efforts to build a fence meant to slow illegal immigration.

Homeland Security Secretary Michael Chertoff said he would give landowners 30 days to indicate if they will allow federal officials on their land to survey whether it is suitable for fencing. If they decline, he said, he would turn to the courts to gain temporary access.

If the agency determines the land is appropriate for fencing and landowners refuse to cooperate, the department will turn to the courts to get title.