(Reuters) -- The U.S. Congress has cleared the way for global miners Rio Tinto PLC and  BHP Billiton Ltd. to swap land with the government, which will allow them to build a long-delayed $6 billion copper mine in Arizona. First proposed nine years ago, the land swap was tucked into the annual defense policy bill passed by the Senate Friday and the House of Representatives last week. The measure will now be sent to President Barack Obama to sign it into law.

The Resolution copper mine, 55 percent owned by Rio Tinto and 45 percent owned by BHP Billiton, could produce more than 1 billion pounds of copper a year at its peak, which would make it the largest copper producer in North America and one of the biggest in the world, according to its online site.

Rio and BHP need the land exchange, long opposed by environmental and Native American groups, to develop the massive underground mine, where the companies have already spent more than $1 billion on drilling and digging a 1.3-mile shaft.

The mine development plan, submitted a year ago, has yet to be approved by the government.

The Resolution project was picked up by BHP in its disastrous acquisition of Magma Copper in 1996.

(Reporting by Sonali Paul in Melbourne; Additional reporting by David Alexander in Washington; Writing by Susan Taylor; Editing by Sandra Maler)