It's a pop dogfight. One of the three original lead singers of Three Dog Night is suing the other two, alleging they are defrauding the public by using the group's name and performing such hits as One (Is the Loneliest Number), Old Fashioned Love Song and Joy to the World. Chuck Negron's suit seeks unspecified damages from bandmates Daniel Hutton and Cory Wells and business manager William McKenzie. He contends it was his distinctive voice that was responsible for the success of Three Dog Night, which sold more than 90 million albums in the 1960s and 1970s. The band broke up in 1977 and reunited in 1981, but Negron had problems with drugs and alcohol. Although he has overcome his dependencies, Negron said, Hutton and Wells had shut him out of the band. Rocker Gregg Allman is suing Capricorn Records for copyright infringement involving 10 albums by the Allman Brothers Band, which he co-founded in the 1960s.