CHICAGO  Defying Senate leaders in Washington and a galaxy of political leaders here, Gov. Rod R. Blagojevich of Illinois announced Tuesday that he would fill the Senate seat of President-elect Barack Obama, which he has been accused of trying to sell.

Mr. Blagojevich said he would appoint Roland W. Burris, a former state attorney general who was the first African-American elected to statewide office in Illinois. The decision set off efforts to block the move by state legislators, the secretary of state, and, most significantly, Democratic leaders in the United States Senate who said they would not seat anyone Mr. Blagojevich chose.

Still, even as the selection was clearly destined for battles on many fronts, Mr. Blagojevich sounded breezily confident as he introduced his appointee to reporters as the “next United States senator from Illinois.” Having been charged this month with conspiracy to commit fraud and bribery, he said the accusations against him should not taint Mr. Burris, whom he called “a good and honest man.”

Standing beside him, Mr. Burris, who, at 71, is seen by many here as an elder statesman in Democratic politics, seemed to brush aside gaping questions about how federal criminal charges against Mr. Blagojevich might tarnish his potential Senate tenure  and whether he would really ever make it to the Senate chamber in the first place.