He opposes abortion, has fought gay marriage and backed Republicans — and soon, City Councilman Ruben Diaz Sr. could be a political neighbor to far-left firebrand Alexandria Ocasio-Cortez.

Diaz, known as much for his trademark cowboy hat as his socially-conservative leanings, is considered the favorite to succeed retiring Rep. Jose Serrano and capture The Bronx’s 15th District, which abuts the 14th District held by AOC.

But political insiders told The Post they expect Ocasio-Cortez to leverage her profile in an effort to keep Diaz — a Democrat currently representing the South Bronx on the City Council — from ascending to national office.

“If there’s a clear alternative to Diaz, AOC will certainly get involved,” said one progressive leader, who requested anonymity.

Added gay-rights activist Allen Roskoff, head of the Jim Owles Liberal Democratic Club, a progressive LGBT organization: “AOC will have a moral obligation to do whatever she can to stop Diaz. We can’t have an anti-choice, homophobic nut get elected to Congress.”

A spokesman for Ocasio-Cortez declined to comment on whether she would attempt to turn the tide in her neighboring district.

Despite his controversies — including his claim in February that the City Council is “controlled by the homosexual community” — Diaz is considered the front-runner to snag the seat.

“Diaz’s name recognition is off the charts,” said Roskoff of the 76-year-old Pentecostal minister, whose son, Ruben Diaz Jr., is the Bronx Borough President.

Even Diaz’s presumptive chief rival, gay Latino Councilman Ritchie Torres, acknowledged that he faces an uphill fight.

“If the election were held today, the reverend would win on sheer name recognition,” said Torres.

The quandary for the left is that as many as nine candidates — among them former Council Speaker Melissa Mark-Viverito and Bronx State Assemblyman Michael Blake — could end up on the ballot, creating the potential for far-left candidates to cannibalize each other’s votes and open the door for Diaz.

“Right now, Ruben is the candidate to beat. All the other candidates are going to split the progressive, liberal vote,” predicted state Assemblyman Jose Rivera, a former Bronx Democratic Party chairman who was raised in the borough’s Hunts Point neighborhood, part of the 15th congressional district.

Torres said that despite Diaz’s early lead, he was confident he would carry the district over Diaz, who he called “a Trump supporter and has backed Republican candidates.”

Diaz supported Republican Rob Astorino over Andrew Cuomo for governor in 2014, and brought then presidential hopeful Sen. Ted Cruz (R-Tx.) to campaign in his district in 2016.

“I’m honored to be the front-runner — but everybody is going to shoot at me now,” Diaz told The Post on Sunday. “I’m here to win.”

Even though Ocasio-Cortez could prove to be a thorn in his side throughout the campaign, Diaz indicated he was open to reaching across the ideological gulf between them.

“I will work with anyone — including AOC — to benefit the people of the 15th Congressional District,” he said.

Additional reporting by Aaron Feis