* Baer heads antitrust practice group at Arnold & Porter

* Baer would replace Sharis Pozen at DOJ's antitrust unit

By Sarah N. Lynch

WASHINGTON, Feb 3 (Reuters) - William Baer, an attorney with the law firm Arnold and Porter LLP, was nominated by President Barack Obama on Friday to head the Justice Department's antitrust division.

Baer, who is the chair of Arnold and Porter's Antitrust Practice Group, also previously headed the Federal Trade Commission's competition division when it stopped a merger between Staples and Office Depot in 1997.

He will replace Sharis Pozen, the acting assistant attorney general for antitrust, who plans to step down at the end of April. Pozen succeeded Christine Varney, who left last August.

Baer's nomination, which was widely expected, still must be confirmed by the U.S. Senate.

The antitrust division of the Justice Department reviews mergers to make sure they comply with antitrust laws, and it also prosecutes price-fixing.

Last year, the division successfully opposed AT&T Inc's $39 billion deal to acquire wireless rival T-Mobile USA , and in May it threatened to sue if NASDAQ OMX Group and IntercontinentalExchange Inc proceeded with a bid for NYSE Euronext.

Baer is seen as someone who would continue the present policies of the Justice Department's antitrust office.

The division's key outstanding cases include the purchase of Nortel's patent assets by a consortium led by Apple, and Google's purchase of Motorola Mobility. It also has a number of criminal price-fixing probes.

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