A retail group controlled by Mexican billionaire Carlos Slim Helu and his sons said today that it will buy CompUSA, the struggling U.S. computer retailer, in a deal that positions the Slims for further penetration into hemispheric markets for Internet-related businesses.

The deal also strengthens a partnership between the Slim family empire and Microsoft Corp., which becomes a minority owner of CompUSA. The two enterprises agreed in October to jointly launch a Spanish-language Internet portal.

The Slim enterprises already include Telefonos de Mexico SA, the privatized national phone firm known as Telmex, and Prodigy, the U.S. Internet provider. Adding a U.S. computer retailer with online and store sales channels could aid cross-border synergies in selling consumer technology, analysts said.

By purchasing CompUSA for $798 million in cash through its Grupo Sanborns subsidiary, the Slims also will put to the test in the U.S. market their turnaround skills, honed over three decades in Mexico's turbulent economy.

CompUSA's share price rose 40 percent today, closing at $9.50 on the New York Stock Exchange. Grupo Sanborns shares, which trade separately on the Mexican bolsa, soared 6.1 percent. Sanborns, which already owned 14.8 percent of CompUSA, controls the Sanborns retail chain, which is leading the foray into e-commerce in Mexico.

The Slim family's successes include Sears de Mexico, bought in 1997 and built into one of Mexico's premier retailing operations. Such deals have made Carlos Slim Helu, 59, Latin America's richest man and the 27th wealthiest in the world, according to Forbes magazine.

Dallas-based CompUSA has 217 stores with 20,000 employees. It has closed a number of unprofitable branches and cut jobs as profit margins on personal computers have fallen. The firm lost $45.7 million in its most recent fiscal year.