For nearly a quarter-century, Senator Joseph I. Lieberman has been an unmistakable presence in a legislative body filled with colorful personalities and large egos.

But on Wednesday afternoon, Mr. Lieberman arrived in the Senate chamber to deliver what he declared would be his farewell speech.

The senior senator from Connecticut, who is retiring in January after four terms, spoke for some 20 minutes on the floor of a chamber where, at various points in his career, he was an outspoken leader on matters like cultural decency, bipartisanship and the war on terror.