A special master overseeing the Justice Department's effort to stop AT&T from buying rival T-Mobile USA has issued a schedule for lists of trial witnesses to be drawn up, according to court papers.

AT&T Inc previously complained that the Justice Department was taking too much time in naming its witnesses as the government seeks to block the telecommunications giant's $39 billion acquisition of T-Mobile USA from Deutsche Telekom AG.

The math on the number of possible depositions and the looming February 13 trial date raise very serious concerns, the special master, Richard Levie, said in an order issued on Sunday.

Levie has been asked by Judge Ellen Huvelle to aid in management of the Justice Department's lawsuit, which was filed August 31.

The government will have to name up to 18 potential witnesses on November 16, with additional witnesses named on December 5 and Jan 6. AT&T will name up to 18 witnesses on November 23, with additional witnesses named on December 12 and January 6, according to Levie's schedule.

Each side will be allowed about 35 witnesses. The trial begins February 13.

Acquiring T-Mobile would vault No. 2 ranked AT&T into the leading position in the U.S. wireless market. The current industry leader is Verizon Wireless, a venture of Verizon Communications Inc and Vodafone Group Plc.

Sprint Nextel, the No. 3 U.S. carrier, and another competitor have also sued to stop AT&T's acquisition of T-Mobile, the No. 4 U.S. operator.

In addition to concerns about market concentration, the government believes the loss of T-Mobile could push up wireless prices since T-Mobile generally costs less than other carriers.

AT&T argues the deal will accelerate its expansion of high-speed wireless service to nearly all Americans.

The Justice Department had no comment on Levie's order. AT&T did not immediately respond to a request for comment.

The cases are USA v. AT&T, T-Mobile USA Inc and Deutsche Telekom AG, case No. 11-1560; Sprint Nextel Corp v. AT&T Inc et al, No. 11-1600; and Cellular South v. AT&T, No. 11-1690. The three challenges are all before the U.S. District Court for the District of Columbia.

(Reporting by Diane Bartz; editing by John Wallace)

Verizon Communications Inc. T-mobile AT&T