Sen. Barbara Mikulski (D-Md.), who has served in Congress longer than any woman in history, will announce at a news conference Monday that she is retiring from the Senate after five terms in office, three people familiar with her plans said. Mikulski, 78, was the first woman to chair the powerful Appropriations Committe, a post she had to give up this year when the Democrats lost control of the Senate. A social worker turned politician, she has been a forceful presence on many pieces of legislation, passionately liberal on certain issues but also committed to working closely with Republicans.