The leaders of four political parties in Suffolk County have been scheming to deprive voters of their right to an honest election this fall. “Honest” means candidates who actively campaign and have their ideas, visions and qualifications tested in the crucible of a truly contested election.

Stop the deals. Stop the cross-endorsements. Stop rigging every race.

This appalling arrogance is not new, but it’s especially despicable this year when two countywide offices on the ballot, district attorney and sheriff, have been tainted by allegations of corruption.

District Attorney Thomas Spota is retiring under a cloud of claims that he used his office to favor his friends and wound his enemies. There is a federal investigation into some of his top aides. Spota empowered James Burke, a close friend who worked in his office before becoming Suffolk police chief, and failed to prosecute him when Burke abused a criminal defendant. Burke was later convicted on federal charges in that incident.

Spota, a Democrat, departs after four terms. And don’t forget that he came into power by leveling corruption allegations against a Republican incumbent, James Catterson, who like Spota often was cross-endorsed by multiple parties. So for the first time in 28 years, voters could have real options in November.

Instead, what’s happening behind the scenes are frenzied negotiations as party bosses try to eliminate any real choices for the two major offices. Democratic chair Rich Schaffer admitted as much in a Newsday story. And GOP chair John Jay LaValle, who two years ago stopped cross-endorsements with the Democrats, is considering lifting his ban. Critics in his party called it “unilateral surrender.”

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The minor-party bosses, Frank MacKay (Independence) and Frank Tinari (Conservative), often back major-party candidates in return for help in races for judgeships, county legislature and town councils. When they’re not trading their ballot lines, the deal is to nominate a faux candidate who will not campaign and is sure to lose. Meanwhile, the snookered voter thinks there was a real choice. Schaffer is a master of this art. State Democrats contend he always refuses to back a strong slate of candidates against GOP state senators. The machinations involving the race for Suffolk sheriff illustrate what is going on. Sheriff Vincent DeMarco is completing his third term, but he won’t have the opportunity to seek a fourth because his Conservative Party is seeking revenge for his decision to take payroll-fraud evidence against then-party chairman Edward Walsh to federal prosecutors, who tried and convicted him.

Meanwhile, Republicans wanted to endorse DeMarco, who won their primary in 2013, but Conservatives balked, threatening to withhold their line from the GOP in other races. So State Sen. Phil Boyle, a Republican, will likely get the GOP, Conservative and Independence lines. And Democrats will nominate a placeholder because Schaffer wants Conservatives to support his district attorney candidate or, at least, withhold support for GOP nominees for district attorney and county legislature.

There is only one way to stop this nonsense: a state law barring cross-endorsements. Third parties should present candidates who compete on the strength of their ideas, not serve as a vessels to exploit or be exploited for the spoils of patronage. — The editorial board