The prospects of closing Guantánamo Bay before the end of the Bush administration are dimming as the Pentagon struggles to find a solution on shutting the controversial prison, according to former and current ­officials.

Robert Gates, the defence secretary, told Congress in September that his push to close Guantánamo had run into “obstacles” from administration lawyers. But he assured senators the Pentagon was drafting a proposal that he hoped the administration would approve and then send to Capitol Hill.