WASHINGTON—Congress's last-gasp deficit-cut talks broke into two tracks Friday, with members of a special committee continuing to seek an elusive $1.2 trillion deal while party leaders discussed a smaller, backup plan in case they fail.

Talk of a Plan B reflected the bleak outlook facing the committee as it heads into its final days. It technically has until Wednesday, but the real deadline is midnight Monday, since members by law need 48 hours to scrutinize any plan before voting on it.

If...