Gov. Spitzer’s second annual State of the State message yesterday featured what may ultimately stand out as his Nixon-goes-to-China moment. Annoying a powerful ally – and embracing a concept he had rejected during the 2006 gubernatorial campaign – Spitzer said he would form a special commission to recommend a “fair and effective cap” on school taxes in New York.

“A tax cap is a blunt instrument, but it forces hard choices and discipline when nothing else works,” the governor said.

Exactly. That’s why the very idea of capping school property taxes drives the state’s public-education establishment right up the wall. And it’s why New York’s statewide teachers union killed a proposed tax cap in then-Gov. George Pataki’s original School Tax Relief package in 1997.

It’s not unprecedented for a union-friendly Northeastern Democrat to advance a school-tax cap; New Jersey’s Gov. Jon Corzine signed one into law just last year. But Corzine was already neck-deep in a fiscal tsunami, desperately hoping to fend off a taxpayer backlash. In a New York state context, Spitzer’s willingness to put a tax cap on the table in Albany is daring.

Spitzer’s first-year stab at the property-tax issue was simply to expand STAR, linking the added benefit to homeowner incomes and letting the Legislature convert it into a rebate check. But in one of his more refreshing passages yesterday, Spitzer punctured the pretense that STAR is actually any kind of solution to the problem:

“A rebate check may temporarily ease the pain, but it doesn’t cure the disease,” he said. “In the end, it’s a losing game for the taxpayer if the state gives you a rebate check on Monday – and then on Tuesday your local government taxes it away.”

So now it will be up to the commission, and particularly its chairman, Nassau County Executive Thomas Suozzi, to recommend a tax cap that will actually protect taxpayers. For a basic model, the panel should look no farther than neighboring Massachusetts, where voters enacted the Proposition 2½ cap on local property taxes 27 years ago.

As of 1980, “Taxachusetts” had the nation’s second-heaviest tax burden, trailing only New York. Homeowners were saddled with property taxes approaching the sky-high Empire State norm. But today, the Bay State tax burden ranks 28th, below the national average.

Property taxes on homes in Boston suburbs are typically thousands of dollars lower than those on comparably priced properties in the New York metro area. Yet Massachusetts public schools haven’t suffered – in fact, they generate the nation’s highest test scores.

The Massachusetts record, and that of other tax limitations around the country, suggest several key benchmarks for Spitzer’s commission to follow in crafting an effective policy in New York:

1) Cap total levies, not individual assessments: Limiting individual property tax assessments, as California’s Proposition 13 did, leads to huge disparities and inequities. Concentrate instead on capping the total amount that districts can raise in property taxes.

2) Aim low: Don’t simply accommodate the average long-term growth in school costs, or you’ll end up with a “cap” of 7 or 8 percent. The best approach remains the growth rate allowed in Pataki’s original STAR cap proposal: 4 percent or the regional consumer price index, whichever is lower.

3) Give voters a veto: Following the lead of Proposition 21/2, New York should allow voters to override caps; taking a leaf from New Jersey’s book, a supermajority of at least 60 percent should be required to exceed the cap.

But exclude the added spending from the base of operating costs used to calculate state aid: If residents of a particular district have rich tastes, let them dig into their own pockets to cover them.

4) Thou shalt not “target”: Resist the (all too likely) political pressure to impose tax caps for residential property alone; or to carve out special savings for property owned by favored groups, such as the elderly; or to establish different caps for different school districts. Moreover, don’t exclude any category of spending from the cap. This would defeat a key aim of local tax limitations-which is to force the governor and legislators to confront the fiscal consequences of the mandates they now impose on school districts.

Many questions remain – not least of them the makeup of the commission, which is also supposed to delve into the “root causes” of high taxes and “how to make our tax relief system fairer to the middle class taxpayer.” If the panel ignores labor-related contractual mandates, it will be a sign that the effort is not serious.

“Let’s finally get real about property taxes,” Spitzer told the Legislature yesterday. If he really means it, he will do much to restore his credibility. But after raising expectations, if the result turns out to be a phony cap and “mandate relief” recommendations that steer clear of sacred cows, it will be worse than if he hadn’t tried at all.