When Robert Morgenthau announced last month that he would retire as Manhattan's district attorney, it marked the end of a remarkable era. Morgenthau, 89, was first elected to be Manhattan's prosecutor in 1974. His retirement also marks the end of nearly a century of public and communal service by three generations of this esteemed New York family. Originally from among "Our Crowd" - non-Zionist Jews of German descent - these three generations of Morgenthaus were mavericks and crusaders on behalf of the weak and of victims of genocide. Morgenthau's grandfather, Henry Sr., was the American ambassador to Turkey who protested the 1915 Turkish massacre of Armenians. "Why are you so interested in the Armenians? You are a Jew; these people are Christians," a Young Turk asked. "Why can't you just let us do with these Christians as we please?" But Henry Sr. was relentless, and to this day is revered in Armenia for railing against the genocide. And although Henry Sr. believed the Jews of America had found their Zion here, he raised $50,000 within weeks in 1914 for some 80,000 Jews who faced starvation because of the war blockade of Palestine. Robert Morgenthau's father, Henry Jr., was president Franklin D. Roosevelt's treasury secretary who, in 1944, accused the State Department of "willful attempts to prevent action from being taken to rescue Jews from Hitler." Roosevelt then created the War Refugee Board, giving it special powers to rescue and aid Nazi victims. Yes, it was too little, too late by the US government, but Henry Jr. made certain the State Department was called to account. WITH ROBERT Morgenthau's retirement, there are accolades about his work as a prosecutor; even his office's successful convictions of the wrong suspects are viewed in admiring terms for the ways in which Morgenthau corrected legal errors. In a 2005 editorial, The New York Times had opposed Morgenthau's bid for reelection - saying he had given Manhattan a "world-class" DA's office but, after three decades, it was time to go. Four years later, when the DA announced he would not seek reelection, the Times spoke of his legacy, commending Morgenthau in an editorial, saying that "his core instincts about the need for fairness and humanity in the law outweighed everything else." This is the family's legacy: fairness and humanity. The art world is still reeling from Morgenthau's exercise in fairness in January 1998, when he detained two Egon Schiele paintings on temporary loan from Vienna to the Museum of Modern Art in New York. Two families claimed the paintings had been seized in Austria by the Nazis. One painting is still the subject of a federal court case. Morgenthau's action put every museum in the world on notice that it must review the artworks among its collection and identify those that once belonged to Nazi victims. "I didn't view our involvement in the paintings as a Jewish issue. It is a stolen property issue. Possession of stolen property is a crime," he told The Jerusalem Post at the time. As a public servant of the Jewish community, Morgenthau is the indomitable chairman of Manhattan's Museum of Jewish Heritage, which opened in 1997. Many thought it would never be built; but built it was, at the southern tip of the city, blocks from the World Trade Center, with the Statue of Liberty as a backdrop. He saw the museum as "a symbol of the power of renewal after catastrophe, and the ability of the Jewish people to survive and endure." David Marwell, the museum's director, recalled having lunch with Morgenthau in 2001 shortly after the September 11 attacks. "He told me to reopen the museum as soon as possible and to continue with our plans to build the new wing," Marwell said. "He was confident about the future at a time when that was a rare commodity." Two years after September 11, the museum opened the "Morgenthau Wing." The museum's expansion was the first new construction project in Lower Manhattan after the terror attacks. "This project began as the dust was still being settled and quickly became an important part of rebuilding Lower Manhattan - bringing jobs and restoring a sense of normalcy," Mayor Michael Bloomberg said at the 2003 dedication. "Robert Morgenthau's tenacity sent a message that our spirit will not be crushed." JEWS HAVE mixed sentiments about dynasties. In the past, the Court Jews or the great banking and trading families were protectors, the natural community leaders whose heirs also inherited communal obligations. These days, however much we need and admire philanthropists, we do not anoint them as kings whose children inherit the realm. The Morgenthaus were in a different class. The three generations were talented public servants who balanced civic and communal roles with principle, poise and passion. This past century was a perilous one. The Morgenthaus were essential participants who went about their missions, not with the exaggeration or grandstanding we have seen from many communal officials, but with a dogged determination to do what is right and just. About 10 years ago, I interviewed Morgenthau for a profile. Among the mementos, certificates and photos that covered every bit of space in his office were artifacts from his navy days during World War II. One - a hand-drawn "proclamation" decorated with a drawing of a mermaid - commemorates that the USS Harry F. Bauer, on which Morgenthau was the executive officer, "survived 79 days at Iwo Jima and Okinawa." After another of his ships was torpedoed and sank, Morgenthau made a vow while swimming in the Mediterranean, without a life jacket. If he survived, he pledged, he would devote himself to public service. Pledge honored. Honorably so.