NEW YORK — I have written repeatedly on Willard Mitt Romney’s serial flip-flops. Mitt is the born-again supply-sider who today swears he never raised taxes, even though he increased taxes and fees $983 million as Massachusetts governor. He is 2008’s stalwart defender of traditional values and man-woman marriage who, in 2002, distributed a hot-pink flyer among Boston’s gay community that read: “Mitt and Kerry Wish You A Great Pride Weekend! All citizens deserve equal rights, regardless of their sexual preference.” (Kerry Healey was the GOP nominee for lieutenant governor.) Romney is the Second Amendment enthusiast who brags about being a life-member of the National Rifle Association — “life” beginning in August 2006 — who said in 1994, “I don’t line up with the NRA.”

Pick nearly any topic, and you will find the new and old Romneys as far apart as two pugilists in opposite corners of a boxing ring, ready to knock each other’s lights out.

But nothing prepared me for Romney’s most amazing flip flop of all. Somehow, I missed it, despite months of researching his bipolar record.

During CNN’s January 30 debate from the Ronald Reagan Presidential Library, Romney said, “one of the two great regrets I have in life is I didn’t serve in the military. I’d love to have.” This echoes what he told the Boston Globe last June 24. “I longed in many respects to actually be in Vietnam and be representing our country there and in some ways it was frustrating not to feel like I was there as part of the troops that were fighting in Vietnam.”

Now, as works with almost any subject, search Google or Nexis for “Romney” and “Vietnam” and any date before 2004, when he got serious about pursuing the 2008 GOP nomination.

Voila! There it is, from May 2, 1994. “I was not planning on signing up for the military. It was not my desire to go off and serve in Vietnam,” Romney told the Boston Herald.

This flip flop is much more revealing and far more disturbing than the rest.

It is bad enough to reverse course 180 degrees on public-policy matters such as taxes, gay rights, guns, abortion, immigration, the minimum wage, Ronald Reagan’s legacy, or any of the other topics on which the old and new Romneys clobber each other. At least these are political issues on which, at best, new information and thinking can justify changed views or, at worst, electoral mathematics can explain abandoning one position for another.

But for Romney to somersault on something so personal — his own non-involvement in the Vietnam War — makes one wonder if Romney is any different from an exterior set on a Hollywood back lot: Clean and pretty in the front and all flat, plywood planks in the back.

Today’s Romney says, more or less, “Too bad I was not part of a military quagmire that tragically cost the lives of 50,000 GIs.” Yesterday’s Romney said, more or less, “How fortunate I was not to be part of a military quagmire that tragically cost the lives of 50,000 GIs.”

Conveniently enough, today’s position plays well in a GOP primary filled with hawkish voters, and now led by the Vietnam War hero, Senator John McCain (R – Arizona). Romney’s 1994 comments more snugly suited Massachusetts — a liberal, Democrat-dominated state where such dovish remarks would have gone down well.

If Romney cynically shifted from his old position to his new one on Vietnam service, he is even more cold and calculating than previously thought.

And if he sincerely went from saying in 1994 that he had not desired to go to Vietnam to 2007’s longing to have been there, one wonders if there is anything at Romney’s core but breeze and tumbleweeds.