Hugh Wolff, the National Symphony's associate conductor, was named music director yesterday of the New Jersey Symphony Orchestra. It marks the first major conductorship for the 31-year-old Wolff, who has been at the National Symphony for five years. Wolff will continue here as a guest conductor. He was in San Francisco yesterday to formally receive one of the first two Seaver Conducting Awards, which amount to $75,000 spread over two years and are meant to help promising young American conductors "on the threshold of major international careers" . . .

Actor Richard Thomas had a big day yesterday. He worked two performances of the 3-hour-and-45-minute "The Count of Monte Cristo" at the Kennedy Center and then at midnight was to go to Mel Krupin's for his 34th birthday party, for which his grandmother, Grace Thomas, and other family members drove up from Kentucky in a van . . .

Entertainers Harry Belafonte and Marlon Jackson flew into famine-ravaged east Africa Wednesday with 120,000 pounds of food and medical aid bought with proceeds from the song "We Are the World," and toured a feeding camp in Ethiopia . . .

Sen. Edward Kennedy says in the July issue of Ladies' Home Journal that he has "sincere regrets" about "times of indiscretion when mistakes were made, but I don't find looking back terribly useful." He also said he hopes his children "don't get caught up in negative publicity about him" . . .