Vice President Joe Biden landed in Tokyo on Monday to start an Asia trip where he was supposed to talk about trade and renew America’s vow to turn our gaze to the Pacific. Now, thanks to some brazen Chinese maneuvering, we may need to do more than talk.

Credit the Obama administration for showing resolve in a face­off between Beijing and our allies, Japan and South Korea. Still, many in the region wonder: Does America still have the will to be the world’s superpower?

Last week, Beijing declared large areas above the East China Sea to be part of its airspace, including the air over an archipelago that it wants to snatch away from Japan and a submerged rock that South Korea calls its own.

US officials were incensed. In her first public address in Tokyo, new US Ambassador to Japan Caroline Kennedy denounced China’s “unilateral” declaration, saying it undermines regional security.

Better yet: Though China had demanded that all aircraft entering the zone file a flight plan with Beijing in advance, two US B-52 bombers immediately flew over the contested zone without notice. Following our cue, Japan and South Korea sent in military jets as well, in what seemed like a well-coordinated maneuvering among allies.

Beijing then made some conflicting statements about how it intends to enforce the zone (or not), indicating that America’s muscular response had made its point.

But then we started waffling: It is, after all, still the Obama administration.

After initially telling China in no uncertain terms that it can’t unilaterally declare just any airspace its own, Washington advised US commercial airlines to file their travel plans with Beijing in advance anyway. (Japan and South Korea are a bit puzzled about that latest US move; their commercial lines won’t file.)

Still, Seoul and Tokyo officials that I talk to are generally pleased — and pleasantly surprised — about Washington’s resolve, as displayed in the B-52 flight.

“Looking at events around the globe, the Chinese are perhaps testing to see if America would drop its traditional Asian allies,” a diplomat from the region told me.

President Obama’s zigzagging on Syria registered in Asia, the diplomat said — as did the US concessions in the nuclear deal with Iran, which so angered our longtime Mideast allies like Saudi Arabia and Israel. Indeed, China announced its air-defense-ID zone on the same weekend we signed that pact with Tehran.

So China was apparently testing whether the United States still has the stomach to confront aggression and stand with friends — and got a “yes.”

America won’t back Japan’s claim of sovereignty over what it calls the Senakaku Islands — which China calls the Diaoyu Islands and claims as its own. But as Tokyo has long administered the archipelago, Washington has declared that it’s covered by the US-Japanese defense treaty.

This is more than a clash over fishery, oil and minerals; it’s a skirmish between two powers with deep memories.

Chinese President Xi Jinping harbors wider regional ambitions than his predecessors. (Beijing on Monday announced a moon mission, too.) He’s also upping investments in military hardware, and has long been seen as an ally of the People’s Liberation Army top brass.

Meanwhile, Japan’s Prime Minister Shinzo Abe, a nationalist, has also expanded military budgets, even while cutting other government spending. Now he demands that China rescind its air-defense declaration completely. He plainly hopes to make this confrontation a defining moment for the region.

“We must cooperate with the United States and others to make China understand that becoming a bigger economy or having a bigger military does not entitle them to take these unilateral measures,” a Tokyo official told me, warning that China must be confronted now, or many will suffer from aggression later.

But will America stand up to Beijing even if events require more than an air show over uninhabitable islands? We should.

Yes, China is the largest holder of our debt, but that’s business: Beijing won’t stop buying US bonds until it finds a better investment (and when it does, it’ll stop no matter what else we do).

To his credit, Obama has handled a brewing Asian crisis well so far, but if he really wants to “pivot” to the Pacific (rather than merely use it as an excuse to withdraw from the Mideast and the world generally), he’d better instruct Biden to gently remind Beijing later this week that our military power is superior, and that we’ll use it to defend our allies.