Marvin Liebman, 73, a conservative political fund-raiser and gay rights activist. Liebman spearheaded techniques of mass mail fund-raising. He was a founder of conservative groups, including Young Americans for Freedom and the American Conservative Union. After campaigning for President Ronald Reagan in 1980, Liebman went to Washington as a public relations official for the National Endowment for the Arts and other agencies. Secretive about his sexual orientation for most of his life, in 1990 Liebman decided to announce his homosexuality in a widely publicized letter to his friend William F. Buckley, editor of the National Review. “I am almost 67 years old,” he wrote. “All the time I labored in the conservative vineyard I was gay.” He said he spoke out because of his concern that conservative speeches and fund-raising pitches were becoming increasingly homophobic. In 1993, Liebman became so distressed by such attitudes that he severed his ties with the Republican Party, the American conservative movement and Christianity. “The only identity of which I am absolutely certain,” he said, “is that I am a homosexual in a country that has little patience with us.” He became a strong spokesmen for gay causes and a board member of the Los Angeles-based Gay and Lesbian Adolescent Social Services. On Monday in Washington of heart disease.