A federal judge ruled on Friday that longtime Detroit-area Democratic U.S. Representative John Conyers should appear on an August primary ballot, saying Michigan registration rules that had disqualified him may violate his constitutional rights. Conyers' bid for re-election had suffered a blow on Friday when state officials said errors in his nominating petitions left the 85-year-old politician without enough valid signatures to appear on the primary ballot. He had been required to submit at least 1,000 valid signatures. But he fell short after hundreds of signatures were thrown out because they were gathered by people who were not registered voters in the state. true In ordering him onto the ballot, U.S. District Court Judge Matthew Leitman granted a preliminary injunction against a Michigan law requiring that petition circulators be registered state voters, saying the measure burdened Conyers' free speech and assembly rights. "The state's interest in co