DALLAS — AT&T bowed to U.S. antitrust authorities and withdrew its $39 billion acquisition of T-Mobile USA Monday, ending a nine-month fight to complete a deal many saw as a long shot and leaving both carriers groping for a way forward.

DALLAS — AT&T bowed to U.S. antitrust authorities and withdrew its $39 billion acquisition of T-Mobile USA Monday, ending a nine-month fight to complete a deal many saw as a long shot and leaving both carriers groping for a way forward.

The high-profile defeat came after AT&T had already pulled its application from the Federal Communications Commission and put on hold efforts to fight the Justice Department's suit to block the deal. In the end, the carrier decided it could not come up with a package of divestitures or other tactics to appease U.S. officials that had deemed it anti-competitive and against the public interest.

The move is a setback for AT&T Chief Executive Randall Stephenson, for whom the merger was the first big deal in his four years in the top job. It was a win for the Justice Department, whose antitrust team took an uncompromising position against the deal in August.

U.S. authorities have approved some big mergers during the Obama administration, including Comcast Corp.'s acquisition of a majority of NBC Universal from General Electric Co.

But the Justice Department drew a line with AT&T's deal, arguing that combining the country's No. 2 and No. 4 wireless carriers would harm competition, leaving the market too concentrated, and likely raise prices for consumers.

T-Mobile subscribers, however, still face an uncertain future. The carrier's parent, Deutsche Telekom AG, has made clear it wants to exit the sluggish U.S. market.

Meanwhile, AT&T had seen T-Mobile's spectrum holdings and thousands of cellphone towers as a quick solution to help ease the well-publicized strains on its network. It will now have to find other ways to improve its network.