The showdown is set: A federal judge could decide on Thursday whether more than 700,000 voters are allowed to vote in the Miami-Dade State Attorney’s August election that will effectively decide who is the county’s top law enforcement officer.

Longtime State Attorney Katherine Fernández Rundle will square off against fellow Democrat Rod Vereen on Aug. 14, a race that would have been open to all voters because no Republicans or independents filed to run.

But just before the April filing deadline, two write-in candidates, Michele Samaroo and T. Omar Malone, filed to run. Neither will appear on the ballot.

Under a controversial and much-criticized state elections opinion, their entry served to close the primary race to just 525,890 Miami-Dade Democratic voters, making Aug. 14 the defacto winner-take-all race.

Enter independent Vincent J. Mazzilli, a former Drug Enforcement Administration’s Miami special agent in charge, and Republican Armando Lacasa, a former Miami commissioner.

They filed a lawsuit last month against Miami-Dade’s elections supervisor, saying the “gimmick” candidates have disenfranchised them from the right to vote for the important post.

Thursday’s hearing is before U.S. District Judge William J. Zloch at the federal courthouse in Fort Lauderdale.

Fernández Rundle accuses Vereen’s campaign of running sham write-ins to cut off Republican and independent voters from whom she enjoys general support.

Vereen denies the claim and accuses her of being a “wolf in sheep’s clothing” by urging Republicans and independents to switch to the Democratic party to vote for her. He insists that he will face Samaroo and Malone in the November election if he wins the primary.

Neither Samaroo or Malone have actively campaigned, reported contributions or returned phone calls from The Miami Herald. Samaroo, in her first public comments, told WPLG-10 Michael Putney in an e-mail this week that she is running on her accord because she is upset with the State Attorney’s “prosecutorial decisions … over the last few years.”

In 1998, Florida voters overwhelmingly voted to change the state’s constitution, opening primary races to all voters if a candidate did not draw a challenger from the opposing party or independents in the general election.

But two years later, Secretary of State Katherine Harris issued an advisory opinion that decided that one single write-in candidate could close a primary.

The federal lawsuit points out that the number of campaigns featuring write-in candidates skyrocketed since, and none have come close to winning. The suit also includes a sworn affidavit from Rod Smith, the head of Florida’s Democratic Party, which says that the party is not taking a position on whether the race should be open or closed.

The lawsuit was filed against Penelope Townsley, Miami-Dade’s election supervisor, who is fighting the suit and says the move is “too little, too late.”

By waiting so long to file the suit, “the election has been programmed, ballots have been printed, overseas ballots have been mailed and absentee voters have voted,” Assistant County Attorney Oren Rosenthal wrote in a reply, saying disrupting the Aug. 14 primary would have a “profound and disruptive” effect on the entire ballot.

Rosenthal wrote that Florida lawmakers, not the courts, should decide election law.

The plaintiff’s attorney, Roberto Martinez, says that Zloch could order that Fernandez Rundle and Vereen — along with the blank spaces for voters to write-in Samaroo or Malone — appear on the November general election ballot open to everybody.

In another political twist, Martinez has also suggested that Miami-Dade Mayor Carlos Gimenez has the authority to order the State Attorney primary opened to all voters. Gimenez’s office, however, insists that only the Florida Secretary of State has the authority to do so.

Gimenez is also on the August ballot, in a non-partisan race open to all voters.