The judge assigned to the federal antitrust case that seeks to undo the $39 billion takeover of T-Mobile USA by AT&T wants all parties to appear on Sept. 21.

Judge Ellen S. Huvelle signed an order which also directs the parties to discuss the prospects for a settlement of the case. The hearing would be in Judge Huvelle's courtroom in U.S. District Court in Washington.

The move is part of routine court procedure. Last week, the U.S. Justice Department filed a civil suit seeking to prevent the takeover of T-Mobile, which is owned by Deutsche Telekom, under the Clayton Act, which concerns antitrust issues. The suit claimed the merger would stifle competition.

AT&T, based in Dallas, and T-Mobile, based in Bellevue, Wash., said they would fight the suit. However, both companies said they might be willing to change parts of their contract to win government approval. The agreement includes a $3 billion cash payout by AT&T, along with services valued as high as $3 billion, if the deal fails.

On Tuesday, Sprint Nextel filed a similar suit, charging a combination of AT&T and T-Mobile would create a player that would be too big for competition. Verizon Communications, the current No. 1 in wireless, has not filed any lawsuits.

Judge Huvelle was appointed to the federal bench by President Bill Clinton in 1999. Previously, she was a judge in District of Columbia Superior Court.

AT&T shares rose 7 cents to $27.90 in Wednesday trading.