Nassau County District Attorney Upends Race for House Seat Kathleen M. Rice, who has won national attention with crackdowns on drunken driving, has said that she will seek the seat being vacated by Representative Carolyn McCarthy, who is retiring. When Carolyn McCarthy, among the nation's most recognizable champions of gun control, announced this month that she would be retiring from Congress after 18 years, a number of names of possible Democratic successors were floated in Nassau County political circles. But the woman who stepped into the race this week may be too formidable to stop. With Ms. McCarthy at her side at a Westbury diner, Kathleen M. Rice, the county's district attorney, revealed on Wednesday that after winning three elections for her job, the last one in November by a margin of more than 17 percentage points, she will seek Ms. McCarthy's seat in the fall election. As Nassau's only countywide Democratic officeholder, Ms. Rice would bring strong credentials and fund-raising prowess to a race for the Fourth Congressional District seat, which covers the county's southwestern corner, including all or parts of Hempstead, Freeport, Roosevelt, Oceanside and Valley Stream. Democrats hold a large edge in registration. "I've spent a career advocating for families," Ms. Rice said in a telephone interview on Thursday. Congress needs an independent problem solver who cares about people and not politics. And that's why I'm running. Ms. Rice, 48, who made her announcement in interviews with Newsday and NBC 4 New York, has won national attention for her crackdown on drunken driving, charging two motorists with murder through depraved indifference. She also reduced the maximum blood alcohol level at which she would accept a plea bargain, and fought for tougher state penalties for those who drink and drive with children in the car. She gained exposure in 2011 when her office arrested seven students in an SAT cheating scandal. One of 10 siblings in an Irish Catholic family in Garden City, she has proved her ability to generate votes, winning her first district attorney's election in 2005 against a 30-year incumbent, Denis E. Dillon. But she has also been criticized by fellow Democrats in the county, like Jay S. Jacobs, the party leader there, for not being tough enough with politicians in Nassau's byzantine swirl. In October, a 29-year-old man was arrested on a public bus by three county police officers on charges he had failed to pay a $250 fine for selling counterfeit DVDs. It turned out that the unusual police turnout came about at the request of the police commissioner and that the man, Randy White, had testified that he was paid, illegally, per signature to gather petitions for the candidacy of Andrew Hardwick on an independent line. The candidacy was largely financed by Gary Melius, a major financial backer of Nassau politicians of both parties, and was seen as a stratagem for siphoning black votes from the Democratic challenger, Thomas R. Suozzi, in his race with Edward P. Mangano, the Republican county executive. Ms. Rice issued a report chronicling the episode and the police commissioner, Thomas Dale, resigned. But Mr. Jacobs issued an 11-page letter criticizing her for conducting an inadequate investigation and for not prosecuting anyone, particularly on charges of witness intimidation. Ms. Rice, whose office website claims she brought more than 80 prosecutions for official misconduct, responded in the interview on Thursday: "As a D.A., I don't make decisions based on political considerations. People want a D.A. that exercises a level of political independence whereby you make decisions based on the facts and the law. Mr. Jacobs said on Thursday that while he was not endorsing anyone he was "very much looking forward to seeing her in Congress," yet adding that she will "have to overcome tensions in the party" over the investigation. Other Democrats considered possible candidates include Kevan Abrahams of Freeport, the County Legislature's minority leader, and Patricia Norris-McDonald, the mayor of Malverne. Ms. McCarthy, 70, has been undergoing chemotherapy for lung cancer and has been on leave from Congress. She entered politics after her husband was killed and her son severely injured in a mass shooting in 1993 on a Long Island Rail Road train. She issued a statement on Thursday endorsing Ms. Rice. "As the citizens of our congressional district continue to recover from Superstorm Sandy and as the citizens of our country demand leadership in combating gun violence and strengthening the middle class, her brand of independent leadership will not be sidetracked by the paralysis of partisan politics," she said.