The report by the nine researchers, published by the Carnegie Endowment for International Peace, said the most likely outcome for the next two decades showed China narrowing the gap with the United States in military abilities, in areas including building aircraft carriers and stealth fighter jets. At the same time, the report, to be released Friday, said China’s economic interdependence with the United States and the rest of Asia would probably prevent it from becoming a full-blown, cold-war-style foe, or from using military force to try to drive the United States from the region.

 

One of the authors, Michael D. Swaine, an expert on Chinese defense policy, called the report one of the first attempts to predict the longer-term consequences of China’s rise for a region whose growing economic prosperity has been largely a result of the peace and stability brought by American military hegemony. He said one conclusion was that the appearance of a new rival meant that, for better or for worse, the current American-dominated status quo might not last much longer.

 

“We wanted to ask, how should the United States deal with this possibility?” said Mr. Swaine, an analyst at the Carnegie Endowment, based in Washington. “Can the United States continue with business as usual in the western Pacific, or must it start thinking of alternative ways to reassure the region about security?”

 

The other authors included scholars, former government officials and other Carnegie analysts.

 

The report, an advance copy of which was seen by The New York Times, said the consequences of the region’s shifting strategic balance might be felt most strongly by Japan, an Asian economic power that has long relied for its security on its alliance with the United States. The report found that in most projections, Japan would probably respond to China’s growing power by clinging more closely to the United States, as it has done recently during a heated argument with China over islands in the East China Sea that both countries claim. At the same time, despite the stance of its hawkish new prime minister, Shinzo Abe, Japan’s fiscal troubles and political paralysis will probably prevent it from significantly bolstering military spending, as some in Washington have hoped it will do to help offset China’s increasing capabilities, the report said.

 

In the most extreme instances, the report predicted, doubts about the ability or commitment of the United States to remain the region’s dominant military power could one day grow strong enough to drive Japan to more drastic measures, like either embracing China or building its own independent deterrent, including nuclear weapons.

 

For the whole region, the report found the most likely outcome to be what it called an “eroding balance” — essentially, a continuation of the current situation, in which American hegemony is slowly undermined by China’s increasing military abilities and growing willingness to assert its interests. The report said the biggest risk in this environment would be an accidental escalation of a limited dispute, like the current clash with Japan over the disputed islands.

 

At the same time, the report said that for the foreseeable future, China would not follow the former Soviet Union in becoming a global rival to the United States. Rather, it said, China would remain a regional power with a narrow strategic focus on territorial disputes with its immediate neighbors. Even so, the report warned, that would still make it a serious challenge to the United States, which has vowed to increase its military presence in Asia despite budget cuts.

 

“Can the United States maintain its primacy of the past 60 years?” asked Mr. Swaine. “The United States says so, but whether it actually can is not entirely clear.”