Judge tells Grupo to offer contract to Asarco union

* Judge orders Grupo to make proposal to union

* Grupo says still needs more time to negotiate

* Grupo says would assume Asarco's existing union contract

By Emily Chasan

NEW YORK, Nov 13 (Reuters) - The U.S. federal judge, deciding whether Grupo Mexico SAB de CV (GMEXICOB.MX) should be able to regain control of bankrupt U.S. copper miner Asarco LLC, has ordered Grupo Mexico to present a contract to Asarco's union.

Judge Andrew Hanen, who sits in the U.S. District Court in Brownsville, Texas, said in a court order on Thursday that Grupo must make a "comprehensive proposal" to Asarco's United Steel Workers union by Nov. 24.

After a year long takeover battle, Hanen is deciding whether Grupo Mexico or rival Indian bidder Sterlite Industries (STRL.BO) should get control of Asarco, which runs three copper mines in Arizona.

U.S. Bankruptcy Judge Richard Schmidt had twice recommended that the District Court approve Grupo Mexico's $2.4799 billion offer for the company over the offer from Sterlite.

Sterlite's bid, however, has been long-supported by Asarco's union, as the two parties have an agreement for a new contract. Grupo Mexico, however, has been stalled in talks with the union for months.