Neal Sher, a lawyer who for 11 years ran the federal office that rooted out World War II-era Nazis in the United States and moved to revoke their citizenship and deport them, died on Sunday at his home in Manhattan. He was 74.

His wife, Bonnie Kagan, said the cause was most likely cardiac arrest.

Mr. Sher joined the newly formed Office of Special Investigations, the Justice Department’s Nazi-hunting department, as a litigator in 1979 and became its director four years later. Its targets were often individuals who had lied to enter the United States after World War II to conceal their Nazi past.

“We’re going after people who are involved in the most heinous crimes known to modern man,” Mr. Sher told “CBS Morning News” in 1983. “For these people to live freely in the United States is contrary to everything this country stands for.”

The cases Mr. Sher prosecuted or oversaw included those of John Demjanjuk, accused of having been a death camp guard and deported to Germany; Archbishop Valerian Trifa, who, as part of the antisemitic Iron Guard of Romania, was reported to have instigated a pogrom in 1941 against Jews in Bucharest; and Arthur Rudolph, who was accused of “working slave laborers to death” in the V-2 rocket factory in Germany before becoming the project manager of NASA’s Saturn 5 rocket program, which was critical to the Apollo spaceflights.

Mr. Trifa was deported to Portugal, and Mr. Rudolph surrendered his citizenship and agreed to go to West Germany rather than fight deportation. In 1987, the government there said there was insufficient evidence to justify trying him.

“O.S.I. had a job that many thought was impossible to accomplish, and Neal showed it could be accomplished,” former Representative Elizabeth Holtzman, Democrat of New York, said by phone. Ms. Holtzman, as chairwoman of the House Subcommittee on Immigration, led the effort to persuade the Justice Department to take over the government’s pursuit of Nazis from the Immigration and Naturalization Service.

In 1986, Mr. Sher recommended that Kurt Waldheim, a former secretary-general of the United Nations, be denied entry into the United States because of his service as a German Army lieutenant in the Balkans during brutal campaigns against Yugoslav partisans and mass deportations of Greek Jews to death camps.

In a report to Attorney General Edwin Meese 3d, Mr. Sher wrote that “if Mr. Waldheim were in this country, O.S.I. would seek approval to institute deportation proceedings on the basis of such activities.”

A year later, Mr. Meese put Mr. Waldheim — who had been elected president of Austria by then — on a list of people who were barred from entering the United States. Mr. Waldheim died in 2007.

Few cases facing Mr. Sher were more complex than the one against Mr. Demjanjuk. Born in Ukraine, a Ford Motor plant worker living in Cleveland. The O.S.I. said he had concealed his war crimes in his immigration papers and accused him of being “Ivan the Terrible,” the sadistic guard at the Treblinka death camp in Poland. He was stripped of his citizenship in 1981 and extradited to Israel, where he was convicted of war crimes in 1988 and sentenced to death.

But in 1993, the Israeli Supreme Court overturned his conviction, citing reasonable doubt that he was “Ivan the Terrible.” An American appeals court panel later that year revoked the original extradition order and criticized the O.S.I. for what it said was a “win at any cost” zeal in prosecuting Mr. Demjanjuk. The office, it said, had failed to turn over to his defense potentially exculpatory evidence that another Ukrainian, Ivan Marchenko, was “Ivan the Terrible” and had shown “reckless disregard for the truth.”

Eli Rosenbaum, who succeeded Mr. Sher as O.S.I. director, said in an interview that while Mr. Sher did not try the case, “He had the misfortune of being director when a lot of details about how the case was mishandled came out.”

Mr. Demjanjuk returned to Cleveland in 1993 and regained his U.S. citizenship five years later. But the O.S.I. continued its pursuit, accusing him of having been a guard at the Sobibor extermination camp in Poland.

“If someone worked at a Ford plant, they made cars for a living,” Mr. Sher told The Los Angeles Times in 2001. “If someone worked at Sobibor, they killed Jews for a living.”

Mr. Demjanjuk lost his citizenship again in 2002 and was deported to Germany. He was convicted in 2011 by a court in Munich for taking part in the murder of 28,000 Jews in Sobibor and was sentenced to five years in prison. He died a year later in a nursing home in southern Germany.

Since 1979, the O.S.I. has deported, extradited or expelled 69 former Nazis.

Neal Matthew Sher was born on Aug. 29, 1947, in Brooklyn. His mother, Sally (Cohen) Sher, was a rent control examiner for New York City’s Housing and Development Administration. His father, Benjamin, a postal worker, had participated in the Normandy invasion in World War II.

Mr. Sher received a bachelor’s degree from Cornell University in 1968 and a law degree from New York University four years later. He clerked for Judge Barrington Parker at Federal District Court in Washington and worked in private practice as a labor lawyer before joining the Nazi-hunting office. The job fed his interests in the Holocaust and the postwar trials of Nazi Germany war criminals at Nuremberg.

As the O.S.I.’s director, he put in place a sophisticated system that allowed the office’s historians to check wartime German personnel records against United States immigration records. The office had previously relied on tips, largely from other governments.

“There is a Hollywood concept about our work that a survivor recognizes his tormentor on the street, which is great cinema,” Mr. Rosenbaum said. “But the reality is more like what we did.”

In conjunction with Israel and Germany, Mr. Sher also led the O.S.I.’s efforts to find Josef Mengele, the notorious death camp doctor. The search led to the discovery in 1985 of a skeleton in a Brazilian graveyard that was determined to be Mengele’s. Mr. Sher himself had urged the German authorities to take blood samples of Mengele’s first wife and son for DNA testing.

He was also successful in ensuring the deportation to Estonia in 1987 of Karl Linnas, the former commandant of a Nazi concentration camp there who had been living on Long Island. Mr. Linnas died that year in a Leningrad hospital after the Soviet authorities had commuted his death sentence.

Mr. Sher left the O.S.I. in 1994 to become executive director of the American Israel Public Affairs Committee, or AIPAC, the main pro-Israel lobbying group in the United States. Two years later he joined a Washington law firm, and in 1998 he was named chief of staff of the International Commission on Holocaust Era Insurance Claims, which settled claims against European insurers by Holocaust survivors and their families.

But in 2002 he resigned when it was disclosed that he had submitted more than $100,000 in false claims for reimbursement of travel expenses. He repaid the money, but the New York bar suspended his license, and the Washington bar disbarred him.

In addition to his wife, Mr. Sher is survived by his brother, Robert. His marriages to Anne Masters and Grazia Lupi ended in divorce.

After being reinstated to the New York bar, one of Mr. Sher’s major cases was representing victims of the mass shootings at Fort Hood in Texas in 2009 by Maj. Nidal Malik Hasan; 13 people were killed and more than 30 wounded in the attack. The victims filed a lawsuit against the federal government seeking benefits and Purple Hearts.

The Army initially put the shootings in the category of “workplace violence,” which prevented the awarding of Purple Hearts. But Mr. Sher argued that the act was domestic terrorism; Major Hasan, who was convicted and is on death row, said the shootings had been an attempt to protect Taliban leaders in Afghanistan from American troops.

Congress ultimately changed the eligibility requirements for the Purple Heart, allowing the victims to receive the medal. Afterward, Mr. Sher said, “I think it finally puts to rest the insulting and disingenuous insinuation that this was an incident of workplace violence.”