The Democratic mayor of Malverne Village Tuesday crossed party lines to endorse Republican Kate Murray for Nassau district attorney, citing her leadership as Hempstead Town supervisor and backing by law enforcement unions.

Patricia McDonald, who recently had been considered by Democratic leaders for potential town supervisor and congressional runs, was joined at a morning news conference by her husband, Steven, an NYPD detective left a quadriplegic by an on-the-job shooting in 1986.

The couple long has been friendly with Murray, Hempstead's supervisor since 2003. Still, Patricia McDonald said she grappled with the endorsement's political ramifications.

"It was not a decision I took lightly," said McDonald, mayor since 2007 of the village, which has about 8,500 people.

But citing multiple endorsements of Murray by Nassau police unions, McDonald said: "It sends a message that she supports our police, and our police need support."

Murray called Steven McDonald "my hero," and said his wife "has worked to keep her community's downtown vibrant." Their standing, Murray said, "makes their endorsement that much more meaningful."

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Murray is running against Democrat Madeline Singas, the acting Nassau district attorney.

"Madeline Singas is a career prosecutor, not a career politician, and she's focused on earning the endorsement of Nassau's voters," campaign spokesman Isaac Goldberg said in response to the endorsements.

Nassau Democratic chairman Jay Jacobs, who backs Singas, said he was "very disappointed" McDonald "wouldn't use her better judgment about who's most qualified, and instead goes to personal relationships. This is a very important position, and while I respect the mayor, and she's a friend of mine, we just disagree here."

Members of Nassau's major parties rarely cross lines for endorsements, although Republican County Executive Edward Mangano last year backed Democratic Gov. Andrew M. Cuomo's re-election bid over the GOP's objections.