Suffolk elections officials have rejected petitions of Fred Havemeyer, who is backed by environmental groups, to wage a Democratic primary against Southampton Supervisor Jay Schneiderman because he did not have 500 legitimate signatures to qualify for the ballot.

Republican and Democratic election commissioners ruled unanimously that 362 of the 699 signatures filed by backers of Havemeyer were not legitimate.

Commissioners also ousted one of two GOP sheriff primary challengers and two Republicans seeking to run legislative primaries. Court challenges must be filed by Wednesday.

Environmental Voters Forum, a political action committee, had backed Havemeyer, a former 12-year Southampton Town trustee and owner of a Bridgehampton horse farm. Havemeyer backers expressed concern that Schneiderman has not taken a strong position opposing The Hills, a 600-acre development in East Quogue.

Vincent Messina, Havemeyer’s attorney, said, “We are weighing all our options.” Schneiderman, an Independence Party member who runs with Democratic backing, said he had not seen the ruling and had no immediate comment.

In the county sheriff’s race, the commissioners ruled against Peter Kraus of West Islip, who had filed petitions to run a Republican primary for county sheriff.

The challenge to Kraus’ signatures was brought by backers of fellow primary challenger Larry Zacarese, deputy chief of the Stony Brook University Police.

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The GOP-designated sheriff candidate is State Sen. Phil Boyle of Bay Shore, who also has Conservative and Independence Party support. Kraus, a retired New York City Police Department sergeant, had no immediate reaction to the decision and could not say whether he would appeal.

Also knocked off the ballot were two other GOP primary challengers, who did not get the needed 500 signatures.

Stephen Ruth of Centereach was seeking to oppose Legis. Tom Muratore of Ronkonkoma in the Fourth District.

Frank Vetro of Miller Place, who was seeking to challenge Gary Pollakuskey of Rocky Point, the designated Republican candidate, to take on Democratic Legis. Sarah Anker in the Sixth District.

Ruth, a critic of Suffolk’s red-light camera program, said he was surprised at the board’s ruling. He said he had filed more than 1,500 signatures. Ruth said he could not say whether appeal until he sees how many signatures were disallowed.

Ruth, who ran unsuccessfully for state senate last year, says Suffolk County has failed to get proper engineering approvals for the camera program. “I’m not a politician, but I’m learning fast and I shall return,” he said.

Vetro, who filed more than 900 signatures, said he does not know how many the board disallowed but vowed to go to challenge the ruling in court. “The objections Republicans raised have never held up in court and they won’t hold up this time,” he said.