Milestones: Jan. 31, 1983

BORN. To William Hurt, 32, intense, hunky, blond movie idol (Altered States, Body Heat), and Sandra Jennings, 26, dancer with the New York City Ballet: their first child, a son; in New York City. Name: Alexander Devon. Weight: 8 lbs. 3 oz.

SENTENCED. Eugene ("Mercury") Morris, 36, former all-pro running back for the Miami Dolphins during the glory years of the early '70s, who was convicted last November on cocaine-trafficking charges; to 20 years in prison, five more than the mandatory minimum. Said Circuit Judge Ellen Morphonios Gable, who pronounced sentence: "George [Yoss, the prosecutor] and I both like Merc, but we've got to do what we've got to do."

DIED. Don Costa, 57, music conductor and arranger, whose versatile professionalism was relied on by top singers of the past three decades, including Frank Sinatra and Barbra Streisand, in concerts, radio, television and more than 240 hit records; of a heart attack; in New York City.

DIED. Sol Spiegelman, 68, pioneering microbiologist whose research on DNA and RNA, the nucleic acids that carry life's hereditary coding, helped lay the foundation for genetic engineering; in New York City. Spiegelman showed how RNA serves as a kind of blueprint whose coded genetic information orders up the production of substances, and also discovered key links between viruses and human cancer.

DIED. Vladimir Bakarit, 70, vice president of Yugoslavia and the last of Josip Broz Tito's comrades-in-arms still in power; after a long illness; in Zagreb. A Croatian lawyer and a Communist Party member since 1933, he joined Tito's partisan army during World War II and served as its political commissar, later rising to membership in the party's ruling Politburo. Under the rotating system of collegial presidency in use since Tito's death, Bakaric was due to become chief of state this spring.

DIED. Joseph H. Lauder, seventyish, cofounder, in 1946, with his wife Estée, of the highly successful cosmetics firm (estimated annual sales: more than $1 billion) that sells her name and formulas and achieved its look of glowing health under his financial stewardship as executive chairman; of a heart attack; in New York City.

DIED. Arturo Umberto Illia, 82, courtly, honest and respected President of Argentina from 1963 until his ouster in a 1966 military coup; of lung disease; in Cordoba City, Argentina. A country doctor by profession, he was elected to the National Assembly in 1948 and dared openly to oppose the dictatorship of Juan Perón. On this national reputation, he was elected President, but his ineffectual administration could not reverse the country's economic slide or prevent the inevitable takeover by disgusted officers.