CANBERRA -- What exactly is America's gripe with China in the South China Sea? The question becomes more and more important as the future of the world's most vital bilateral relationship becomes more and more dependent on what happens in this much-contested waterway. And the answer is not very clear.

The South China Sea has been a point of friction between Washington and Beijing for many years, but over the past few weeks it seems Washington has quite deliberately turned up the volume of its criticisms of Chinese actions there. We have seen an apparently well-orchestrated campaign of official U.S. statements and well-sourced media stories culminating in the much-publicized U.S. Navy P-8 surveillance mission close to China's construction work on Fiery Cross Reef, and Defense Secretary Ashton Carter's forthright speech in Singapore at the end of last month.

The common theme has been that America has decided to take a new and much tougher line -- to draw a "red line" one might say -- to stop what it sees as China's misconduct in the South China Sea. But what is that misconduct? Two sets of concerns have been raised in recent U.S. statements.

The first is China's use of bullying and coercive tactics to press its claims to disputed islands and reefs in the region against those of its smaller and weaker neighbors. Its recent bout of land reclamation falls into this category, according to Washington. The second is what Washington regards as threats to freedom of navigation in the South China Sea. Let's look at these in turn.

There is no doubt that China is throwing its considerable and growing weight around to intimidate and overawe rival territorial claimants. We saw this in its showdown with the Philippines in the Scarborough Shoals in 2012, and with Vietnam over oil drilling in 2014. However, much as we may regret this kind of conduct, it is not contrary to international law.

That may be why U.S. statements have tended to place somewhat greater emphasis on concerns about threats to freedom of navigation. Like motherhood and apple pie, freedom of navigation is one of those concepts which can be invoked to justify all kinds of actions. But what kinds of threats does China pose to freedom of navigation in the South China Sea today?

To clarify this we have to first draw a clear distinction between commercial and military shipping. Both media reporting and official statements often make it seem as though the immense volume of seaborne trade that traverses the South China Sea, and the importance of this trade to regional and global prosperity, is a reason to be concerned about the area's territorial disputes.

Commercial Navigation Not Threatened

But there is no evidence at all that freedom of commercial navigation is in any way threatened by the actions of any of the claimants, including China. Nor is there any reason to fear that any of the claimants might try to restrict commercial navigation there in the future -- least of all China, whose own trade constitutes such a large and growing share of the traffic.

Military navigation, however, presents a more complex picture, because America and China do take different views of some critical issues about military operations in Exclusive Economic Zones. Under the United Nations Convention on the Law of the Sea, which created the concept, 200 mile EEZs only gave a country the right to exploit the economic resources under and in the sea, but they did not affect the rights of foreign ships and aircraft, including military ships and aircraft to pass through or over them. From the U.S. perspective the waters remain international waters for these purposes.

China has long taken a different view. It claims a right to restrict foreign ships and aircraft from undertaking military operations, including surveillance and intelligence collection operations, within its EEZ.

Beijing has at times attempted to enforce this claim by intercepting U.S. ships and aircraft conducting such operations within its EEZ.

For a worldwide maritime power like America, which has always relied on its ability to project power globally by sea and air, this is a significant "freedom of navigation" issue, and many other countries around the world share the U.S. position. On the other hand, China is not alone in placing a more restrictive interpretation on military operations in EEZs, and America's position is somewhat undermined by the fact that it is not formally a party to the UN Convention on the Law of the Sea because successive U.S. administrations have failed to persuade Congress to ratify it.

And one can feel at least a twinge of sympathy for China's position. Imagine how Americans would feel if Chinese military aircraft and ships conducted regular surveillance and intelligence-gathering missions within a few dozen miles of America's Pacific coast.

Moreover, this disagreement between Washington and Beijing is not specific to the South China Sea. It arises throughout China's huge EEZ, which extends right up its western Pacific coastline. So it seems somewhat counterproductive for Washington to raise the issue specifically in relation to the South China Sea where there are already so many sources of tension and friction.

And important though the general issue no doubt is, U.S. policymakers will need to decide at some stage whether it is worth sticking rigidly to their interpretation of the law when a little compromise might make it easier to manage this all-important relationship.

Real Reasons Run Deeper

Indeed, the more closely one looks at the issues in the South China Sea, the clearer it becomes that the concerns America has raised about Chinese conduct are merely pretexts for the "red line" it seems to be proclaiming there. The real reasons run much deeper. They have nothing to do with the South China Sea itself, and everything to do with the much bigger question of who leads in Asia over coming decades. So, too, are China's motives.

China's hard line on these maritime sovereignty disputes is not intended just to enforce its title against those of other claimants. It is also intended to demonstrate China's growing power at sea in the western Pacific, where America has for so long been preponderant. By pushing its maritime claims so assertively against U.S. friends and allies, China is showing the world that it is now a power to be reckoned with in the western Pacific.

From Beijing's perspective, the more China presses U.S. allies and defies U.S. criticism with impunity, the further the credibility of U.S. leadership in Asia falls, and the more China's claims to regional leadership are enhanced.

Washington's policymakers see things differently. They hope that the harder Beijing pushes its neighbors, the more anxious they will become about China's power, the more eagerly they will seek and support U.S. leadership, and the further America's primary position in Asia will be enhanced. That is why they have been talking up these somewhat exaggerated concerns about China's actions in the South China Sea, and talking tough about their determination to push back.

It is not hard to see how dangerous this game can become. Both America and China hope to score points and look strong by making the other side back down and look weak. Both may underestimate the resolve of the other. If so, both will face the choice they hoped to impose on the other, between a humiliating back down and a dangerous and potentially uncontrollable conflict. Both sides need to take steps to avoid that looming disaster. That includes Washington.

Hugh White is professor of strategic studies at the Australian National University in Canberra. His book "The China Choice: Why We Should Share Power" was published in the U.S. in 2013.