AT&T on Monday waved a white flag in its battle to acquire T-Mobile, agreeing to postpone an antitrust lawsuit that it badly needed to win as other options faded.

The decision means the $39 billion merger, as originally proposed, is all but dead, antitrust experts said.

And the move has raised fresh questions about the futures of AT&T and T-Mobile, which have waged all-consuming battles to win regulatory approval of their deal as the competitive landscape has shifted significantly around them.

In the eight months since AT&T launched its quest to acquire T-Mobile, Dish Network has created its own plans to be a wireless carrier, Microsoft bought Skype to offer wireless phone calls over the Internet, and Facebook created an instant messaging service that could substitute for text messaging.

The bruising battle for T-Mobile has left AT&T so far without what it wanted, and now it is facing rivals — particularly its biggest competitor, Verizon — who are even stronger, analysts say.

“Verizon comes out the biggest winner here, quietly sitting on the sidelines but working on big deals for its future as everyone else punches it out,” said Jeff Silva, an analyst at Medley Global Advisors.

AT&T’s move Monday was another bleak sign for the company in its audacious attempt to swallow the fourth-largest wireless carrier. The Justice Department and Federal Communications Commission have opposed the deal, saying it would lead to higher monthly cellphone bills for consumers and less competition.

AT&T had felt its best chance at salvaging the merger would be by fighting a Justice Department lawsuit aimed at blocking the deal.

But last week, Justice said it would withdraw or postpone its suit to ensure the proposal doesn’t get its day in court.

On Monday, the wireless giant asked a federal judge to postpone the suit, in hopes of reworking a deal with T-Mobile that would allay concerns raised by antitrust officials.

“We are actively considering whether and how to revise our current transaction to achieve the necessary regulatory approvals,” AT&T said in a statement Monday.

Judge Ellen Huvelle of the U.S. District Court of the District of Columbia approved the request.

Experts doubted, however, that AT&T would be able to come up with a revised plan to win over regulators. Officials at Justice and the FCC have opposed the deal, saying the combination would put 80 percent of all cellphone contracts into the hands of two carriers — AT&T and Verizon. And even if AT&T were to divest a big chunk of T-Mobile’s business, antitrust officials would still be concerned with how much spectrum — the airwaves used for wireless networks — would go into the hands of two powerful firms.

“It will have to pass a very high bar,” according to a person familiar with the thinking of federal antitrust officials.

AT&T is under immense pressure to salvage the deal.

The company faces a Sept. 20, 2012, deadline to close the venture or pay T-Mobile $4 billion in cash and other wireless assets. The one-month delay could also allow AT&T to renegotiate its breakup fee with T-Mobile, experts said.

“It’s just one more indication of how difficult it’s going to be for AT&T to make this deal come off,” said Bert Foer, president of the American Antitrust Institute. “This is probably the best thing they can get right now.”

Beyond the breakup fee, the companies will probably suffer from recent moves by competitors. Verizon has waged its own business battles to draw away AT&T and T-Mobile’s customers and build better high-speed Internet networks.

AT&T has argued that customers would face dropped calls and slow Web surfing unless it can combine T-Mobile with its own network. T-Mobile’s parent, Deutsche Telekom, said it was too hard to compete in the United States and that it was putting the business up for sale no matter what. Sprint Nextel got into the fight, saying it could not survive as a standalone entity if the merger was approved.

Yet Verizon never opposed the deal and earlier this month surprised the industry with a $3.6 billion plan to buy wireless assets from cable companies in a sweeping joint marketing agreement. The deal poses a challenge for regulators who are already grappling with an array of established and new companies all vying to become the gateway for delivering media and communications to consumers.

But it’s “not entirely clear how [regulators] get their hooks into it even if they wanted to try to stop it,” said Craig Moffett, a Bernstein Research analyst in a recent conference call.

“This is really a strategic masterstroke for Verizon in that it takes an enormous step toward wireless duopoly but does it with far less regulatory friction than the AT&T transaction to buy T-Mobile.”