President Barack Obama will begin budget negotiations with congressional leaders Friday by calling for $1.6 trillion in additional tax revenue over the next decade, far more than Republicans are likely to accept and double the $800 billion discussed in talks with GOP leaders during the summer of 2011.

Mr. Obama, in a meeting Tuesday with union leaders and other liberal activists, also pledged to hang tough in seeking tax increases on wealthy Americans. In one sign of conciliation, he made no specific commitment to leave unscathed domestic programs such as Medicare, leaving the door open to spending cuts many fellow Democrats oppose.