GENEVA, JAN. 9 -- When Secretary of State James A. Baker III faced his Iraqi counterpart Tariq Aziz across the negotiating table today, he was aiming much of his message at a man seated next to the foreign minister: Saddam Hussein's half brother, Barzan Takriti.

U.S. officials have said Aziz, a Christian, is not part of Saddam's inner circle despite his highly visible role as Baghdad's chief diplomat. By contrast, Barzan's influence is known to extend far beyond his official role as Iraq's representative to the United Nations here.

A tough man who once headed Iraq's powerful internal security force, Barzan shares with Saddam the ruthless nature that characterizes their warrior clan from the northern town of Takrit. The genteel diplomatic community here recalls with horror how Barzan, angry about having to wait for his car, once beat up his chauffeur in public at a diplomatic reception.

Over the years, Barzan has been entrusted by Saddam with some of his regime's most important and sensitive tasks. He was Saddam's point man in the drawn-out negotiations with Iran following a cease-fire in August 1988 that ended more than eight years of war.

More recently, Western intelligence sources have said Barzan supervised Iraq's efforts throughout Europe to secure sophisticated technology that could be used to augment its military might. He reportedly masterminded deliveries from German firms of equipment that Iraq used in chemical weapons production.

In addition, Barzan is said to have coordinated Iraq's attempts to acquire key components in the West to build nuclear weapons and the long-range artillery "supergun" that was unmasked by British authorities.

Western officials also have said Barzan has been implicated in systematic harassment of Iraqi exiles in Europe who are opposed to Saddam's regime. Barzan denies any involvement in terrorist activity.