Margaret "Maggi" Henderson, 77, president and partner of the Henderson/Hogan talent agency in New York and Los Angeles. With her partner of 29 years, Jerry Hogan, she was involved in the careers of actors Michael Learned, Tom Selleck, Cleavon Little and Robert Downey Jr., among others. A native of Trinidad, Colo., she grew up in San Diego and graduated from San Diego State and the Juilliard School of Music. She was given the Lifetime Achievement Award by the Assn. of Talent Agents in 1989. "She knows what it means to nurture a career," Center Theater Group artistic director Gordon Davidson said upon presenting the award. "She's a class act." On Friday in Los Angeles of heart failure.