"I think that what we are doing is going after the last universally recognized evil that the world has known," says Martin Mendelsohn, who pauses to consider that sweeping claim, smiles at its enormity, and allows as how that doesn't sound like too bad a job description.

Mendelsohn heads the Special Litigation Unit at the Immigration and Naturalization Service, which is a cool bureacratic name for his real job: chief Nazi hunter for the federal government.

Working with the Israeli police, various federal agencies and informants, Mendelsohn and a team of five attorneys eight months ago began a concerted effort to discover and deport Nazis who slipped into the United States under false pretenses. Previously, the task was assigned to INS investigators responsible for other department functions. But now the buck stops at Mendelsohn's office, which is about to hire its own investigative staff. "I think there was a realization that the problem was bigger than we thought and that in order to get a firm grasp, prosecution had to be centralised," says Mendelsohn, a 35-year-old attorney who practiced law privately before beginning his new job last year.

"It sounded impossible . . . trying to present evidence in legal proceedings involving events that occurred 35 years ago not in this country," says Mendelsohn. The key to successful prosecutions: witnesses who survived the Holocaust, many flown here from overseas to testify, using up a good portion of the unit's $2 million annual budget. Not all witnesses live in Israel; Mendelsohn is awaiting court permission in a case involving a Baltimore man that would require taking depositions from three Jews in Russia. And few of his targets are German. Most of the 169 cases under active investigation or litigation involve Latvian, Yugoslavian, Ukranian, Polish-German, Lithuanian or Romanian natives "because the Germans used people in the occupied countries to do the dirty work."

Mendelsohn says the fact that he's Jewish dosen't intrude on his work; he prefers to think of himself as a sharp trial lawyer ("If you ever come across a modest lawyer, you're not talking to a good one," he says). Father of two children, Mendelsohn lives in Bethesda with his wife, though he suggests a reporter check with his wife to see if he's still married - and his job kept out of town all but a few weekends last month. The grim nature of his work (witnesses, faced with tormentors from decades ago, break down in court as they relive events long repressed) seems not to affect Mendelsohn's out-of-court banter.

"Intense? Who me? The original laid-back guy?" he jokes. "What can I say except don't be deceived - I view this as very significant, serious and important work - it just depends which end of the buzz saw you're on."