The Justice Department said on Friday it would seek to postpone its legal challenge to AT&T's $39 billion proposed acquisition of T-Mobile USA, dealing another blow to the fragile deal.

Justice Department lawyer Joseph Wayland, the lead litigator in the case, said he planned to file the motion next week because AT&T withdrew its filing with the Federal Communications Commission.

AT&T and Deutsche Telekom's T-Mobile said they pulled their application with the FCC last month so they could focus on the Justice Department challenge.

If the judge approves the request, it would push back the trial that is scheduled to start in February. AT&T and T-Mobile USA have sought a quick end to the legal challenge to preserve the value of the deal.

It's not a real transaction until they file with the FCC, he told Judge Ellen Huvelle.

(Reporting by Diane Bartz; Editing by Derek Caney)