Beloved Mets catcher Mike Piazza comes out swinging in a new memoir — confronting rumors about being gay and taking steroids, detailing his romantic home runs and finally settling the score with his hated rival, Roger Clemens.

The book, “Long Shot” (Simon & Schuster) comes a month after Piazza, arguably the greatest hitting catcher of all time, fell 98 votes short of being voted into the Hall of Fame in his first year of eligibility. Many think he missed because of persistent rumors he used performance-enhancing drugs during a 16-year career.

The 44-year-old makes no bones about holding a grudge against Clemens for beaning him during a July 8, 2000, game, and for the infamous bat-throwing incident later that season against the Yankees during the World Series.

The 98-mph fastball to his helmet could have been deadly.

“I truly believe that if I hadn’t gotten my head down at the last instant, Clemens’ two-seamer would have struck me in the eye and possibly killed me,” he recalls.

The Yankees hurler called the Mets dugout to apologize during the game, but Piazza wasn’t hearing it.

“I grabbed [the phone], threw it and said, ‘Tell him to go f–k himself,’ ” Piazza said.

“Roger Clemens had near-perfect control. I wouldn’t have batted an eye if he had just brushed me off the plate — of course that’s what he said he was trying to do . . . But to stick it in my forehead, that’s another story altogether.”

Piazza tells how he mapped out a plan for revenge — taking karate lessons and visualizing the next time they would go at it.

“I would approach with my fist pulled back. I figured he’d throw his glove out for protection. I’d parry the glove and then get after it,” Piazza writes.

He would get his chance in October — when the upstart Mets met their crosstown rivals in the World Series. The coming confrontation between the Mets’ 12-time All-Star catcher and the Bombers’ hard-case hurler was the talk of the city.

The climactic moment came at Yankee Stadium, during Clemens’ fourth pitch to Piazza in the first inning of Game 2. The sizzling fastball sawed Piazza’s bat into three pieces, with a shard flying toward the mound. Clemens picked up the splintered barrel and, inexplicably, chucked it in Piazza’s direction as the hitter ran down the first-base line.

“What the f–k is your problem?” Piazza, still holding the handle of the broken bat and walking toward the pitcher’s mound, asked Clemens. But Piazza went no further — and never realized his dream of revenge.

“There were complications,” he recalls. “The least of them was the realization that Clemens was a big guy, and I stood a pretty fair chance of getting my ass kicked in front of Yankee Stadium and the world. That was a legitimate concern.”

It was a decision over which he still beats himself. “It was not only possible but — circumstances be damned — it was in order,” he said. “It was the story of the Series. I couldn’t deliver a punch.”

Piazza carried a chip on his shoulder toward the Yankees, even off the field.

After a Guns N’ Roses concert, Piazza — who’d been drinking vodka all night — chided lead singer Axl Rose for wearing Rangers, Knicks and Yankees jerseys on stage. But not his team’s.

“I’m obliterated. I go, ‘Hey, yo, Axl! What the f–k, man? Like, you know, you think you could’ve mixed in a Mets jersey?’ ”

The baseball world speculated about Clemens’ apparent “roid rage” during the 2000 Subway Series, and Piazza, late in his career, had to battle similar rumors about using performance-enhancing drugs.

The book, co-written by Lonnie Wheeler, flatly denies this.

“I was into power, not prison,” he said of illegal steroids.

The strongest concoction he admits taking was androstenedione — also called “andro,” a muscle-building supplement bought over the counter at nutrition stores in a “Monster Pak” that also contained creatine and amino acids.

When andro was found in Mark McGwire’s locker in 1998, Piazza said he decided to phase it out of his own regimen. In 2004 the FDA banned it.

Piazza admits that every team had a treasure chest of drugs.

“I used Vioxx because it was an intense anti-inflammatory and it made me feel good,” he writes in the book, which is set to go on sale Tuesday.

“When I caught for 22 straight days and could hardly drag myself out of bed to get to the ballpark, Vioxx picked me up. I’d sing, ‘It’s gonna be a Vioxx morning.’ ”

Piazza admits he took “greenies” — stimulants that were once common in baseball — usually in his coffee. But they made him too jittery. He preferred Dymetadrine, a light asthma medication that sends more oxygen to the brain. He also used Ephedra, an over-the-counter fat burner. It was later added to the banned list.

The use of PEDs was not the only rumor swirling.

Piazza believes the persistent whispers that he was in the closet began after Mets manager Bobby Valentine said in a 2002 interview that Major League Baseball was ready for an openly gay player.

“The whole episode was such a strange, incredible phenomenon . . . I still don’t get it.

“I don’t know where the rumor came from, although I’ve heard many theories, including one that I suppose makes the most sense to me, involving a former teammate and his agent.”

Piazza doesn’t name the instigators, and is vague about how the rumor spread from there. He felt compelled to address the gossip publicly, telling reporters, “I’m not gay. I’m heterosexual. I can’t control what people think. I can say I’m heterosexual. I date women. That’s pretty much it.”

Questions about his sexuality bothered him less than the insinuation that he was somehow phony. “I found it hugely insulting that people believed I’d go so far out of my way — living with Playmates, vacationing with actresses, showing up at nightclubs — to act out a lifestyle that would amount to a charade,” he writes. “If I was gay, I’d be gay all the way.”

Not only is Piazza heterosexual, the book claims, he’s a world-class heterosexual. He managed to stay a free agent throughout his major-league career.

One of his best-known girlfriends was Debbe Dunning, the actress who played the “Tool Time” girl on the hit comedy “Home Improvement.” One Halloween night when Dunning came over with a pumpkin and her dog, Piazza decided to break off the relationship.

“There was screaming and crying and then the Tool Time girl waffled my ass,” he recalled. “I hadn’t taken a punch like that in a long time.”

For several years, it was a new girlfriend for each new baseball season, including Playmate of the Millennium Darlene Bernaola. He finally settled down with another Playmate, Alicia Rickter, in 2005. They have two daughters.

Piazza, who grew up in a Catholic family in suburban Philadelphia, was born into baseball.

His dad’s close pal, then-Dodgers manager Tommy Lasorda, helped Piazza break into the bigs.

As a 14-year-old traveling with Lasorda’s Dodgers to Shea Stadium — Piazza’s first trip ever to the ballpark — the teenager walked into the clubhouse.

“Most of the team was watching a porno film. There was one little TV in the training room, and they were all crowded around it,” he recalls.

“I have to admit that coming from the straight-laced, deeply Catholic background that I did, it was a little unsettling.

“I didn’t tell my mother.”

Piazza made the big show in 1992, and women noticed.

The rookie of the year, then playing for the Dodgers, felt he had a rock-star image to live up to, but his Catholic upbringing was getting in the way.

“Obviously, premarital sex was morally objectionable to the Catholic Church, which, like my very Catholic mother, was still a major influence in my life,” he writes. “On the occasions when I did step out, I made a point of going to confession afterward.”

¡Habla inglés!

Mike Piazza thinks Hispanic ballplayers need to learn English.

“I certainly don’t dispute that Latin players are entitled to the same dreams and opportunities that I had, but I’m sorry: when they arrive on US soil, the onus isn’t on the American players to learn Spanish,” he writes in his memoir. “It’s on the Latin players to learn English.”

Tensions between Piazza and Latin ballplayers simmered more than once during his 16-year career.

Piazza describes “some kind of weird Hispanic conspiracy against me, almost like a secret brotherhood, a Latin mafia-type of thing.”

During his Dodger days, he was scorned by teammates Ismael Valdez, and Ramon and Pedro Martinez. And he was hit by pitches by Pedro and Guillermo Mota, and Julian Tavarez.