Conyers.

DETROIT — Longtime Michigan Democratic Congressman John Conyers’s bid for reelection in November took a major hit on Tuesday when a local elections clerk declared him ineligible for the August primary ballot because he did not have enough valid signatures on a required petition.

Wayne County Clerk Cathy M. Garrett found that 644 signatures submitted on nominating petitions by Conyers’s campaign were invalid because some of the petition circulators were not registered voters, leaving him short of the 1,000 signatures needed.

The liberal Conyers, who will turn 85 on Friday, is one of America’s most prominent African American politicians and a former chairman of the powerful House of Representatives’ Judiciary Committee.

Now in his 25th term, Conyers was first elected to the U.S. House in 1964 and currently ranks second in seniority. Fellow Michigan Representative John Dingell, who is retiring this year, is the “dean” of the House, having arrived in 1955.

Conyers and his aides were not available for comment. He is expected to appeal the clerk’s decision.

The American Civil Liberties Union filed a lawsuit on his behalf in federal court on Monday, saying the state requirement that petition circulators be registered voters is unconstitutional.