Any new moves in the region by China to assert its claims unilaterally would be met by an American military challenge intended to get Beijing to back down.
By ADAM ENTOUS and JULIAN E. BARNES
The question of security in the South and East China seas has dogged President Obama, above in Kuala Lumpur Sunday, during his Asian trip.
WASHINGTON—The U.S. military has prepared options for a muscular response to any future Chinese provocations in the South and East China seas, ranging from displays of B-2 bomber flights near China to aircraft-carrier exercises near its coastal waters, officials said.
The menu of options, described by officials briefed on the action plan, reflects concerns that U.S. allies in Asia have questions about the Obama administration's commitments to its security obligations, particularly after Russia's seizure of the Crimean peninsula.
Washington's closest allies in Asia have told American counterparts that Crimea is seen as a possible litmus test of what Washington will do if China attempted a similar power grab in the South China and East China seas, according to current and former U.S. officials.
"They're concerned. But it's not only about Crimea. It's a crescendo that's been building," a senior U.S. defense official said, citing skepticism in Asia that Washington is prepared to back up its word and carry through on its renewed strategic focus on Asia.
Just before Mr. Obama landed in the Philippines on Monday, U.S. and Philippine officials finalized an agreement allowing for the return of U.S. forces, more than two decades after Philippine opposition forced Washington to abandon its military network there.
Similarly, Mr. Obama in a visit to Japan stood side-by-side Thursday with Japanese Prime Minister Shinzo Abe and called the U.S. treaty commitments to Japan's security "absolute."
On each stop in Asia, including South Korea and Malaysia, Mr. Obama's trip was accompanied by concerns over aggression by Moscow and its militant allies in defiance of warnings by the U.S. and other Western powers.
Similar concerns were raised in September by South Korean officials after Mr. Obama abruptly called off plans to bomb Syria in response to the regime's use of chemical weapons against the opposition.
The new U.S. options were developed by the Hawaii-based U.S. Pacific Command in recent months, and come after the international crisis last year in which China unilaterally declared an air-defense zone around islands that are the subject of a territorial dispute with Japan.
Defense officials said the options have been drafted to apply to any provocative act in the region, whether carried out by China or North Korea.
Defense officials are currently revising the options in the context of a possible act of aggression by North Korea, with some officials arguing Pyongyang is poised to begin a "cycle of provocation."
The Pacific Command, like other U.S. regional military commands world-wide, regularly drafts military options and contingency plans.
The options were recently updated to make them brawnier, defense officials said.
"Combatant Commands plan…for everything from exercises and humanitarian assistance, disaster relief operations all the way up to full-scale combat operations," said Capt. Chris Sims, the spokesman for Pacific Command.
"In the plans that they create, options are provided to senior military and civilian leadership."
In addition to bomber flights and aircraft carrier maneuvers, the options include demonstrations of U.S. power such as increasing surveillance operations near China, and stepping up U.S. naval port visits to allies.
A senior Obama administration official declined to comment on details of any military options, but said unilateral moves by Beijing—such as the declaration of another air-defense zone in the region—" could result in changes in our military posture and presence" in the region.
The military options don't specify particular responses to individual actions.
Rather, officials briefed on the options said, the actions would need to be tailored to the specific incident, such as maritime confrontation.
Under the U.S. options, any new moves in the region by China to assert its claims unilaterally would be met by an American military challenge intended to get Beijing to back down.
U.S. officials said the White House would be prepared to step up military deployments in disputed waters in the South and East China Seas, in a more direct challenge to Chinese claims there than the U.S. has taken in the past.
The steps can be taken without risking a shooting war, officials say, citing intelligence that suggests there are divisions within the Chinese military establishment about how to respond.
U.S. defense officials said some of the options are designed to send a subtle message, like stepped-up port calls by Navy ships or increasing the size and scope of already-planned exercises.
All of the contingency plans, said a defense official, are designed to allow a potential adversary a chance to de-escalate.
"Never push your enemy into a corner because you might get a reaction you don't want," said a U.S. official, specifying the need for an "off ramp."
China has repeatedly said it would respond to American shows of military might in kind.
China has been investing heavily in its military, modernizing its forces and becoming a stronger regional power.
The White House authorized U.S. military aircraft flights in a show of force last year during a spike in tensions with North Korea.
The U.S. also flew B-52s over disputed islands in the East China Sea when China in November established its Air Defense Identification Zone.
Current and former officials said among the more provocative options on the table to counter China would include expanded U.S. surveillance flights and sending U.S. aircraft carriers through disputed waters close to the Chinese coast, including the strait of Taiwan.
The U.S. Navy regularly sends destroyers and cruisers through the strait of Taiwan in lower-profile freedom-of-navigation operations, but sending a carrier through would mark a significant escalation, officials said.
Doubts about U.S. resolve haven't been expressed publicly by Asian leaders during the president's trip.
Under threat from Russia, Kiev earlier this year appealed to Washington for small arms and ammunition, as well as for nonlethal items like flak jackets and night-vision goggles.
Wary of antagonizing Moscow, the White House dragged out internal deliberations for weeks before deciding earlier this month to send helmets, sleeping mats and other nonlethal gear deemed by U.S. officials to be less provocative—but no arms.
U.S. officials say Asian allies who want to know how Washington would respond to future acts of Chinese aggression shouldn't look at what the U.S. is doing to aid Ukraine but instead at Pentagon moves to reassure Eastern European allies and Baltic states since the U.S. is bound by treaty agreements to help defend them.
The Pentagon last week said it is sending several hundred troops for exercises in Eastern Europe, and that it would keep a rotational naval presence in the Black Sea.
A senior military official said the changes were small but "proportional to the threat."
As with its North Atlantic Treaty Organization partners in Europe, the U.S. has defense treaties with Japan, South Korea and the Philippines.
The U.S., in contrast, has no such agreement to defend Ukraine, U.S. officials have told their Asian counterparts.
"It's comparing apples and oranges," said a senior military official.
Like Ukraine, nontreaty allies in Asia would get more-limited support from the U.S., officials said.
U.S. officials have privately warned their Chinese counterparts in recent exchanges, including a visit to Beijing by Secretary of State John Kerry in February, that the U.S. won't accept moves by China to unilaterally declare another air-defense identification zone or to assert Chinese territorial claims in the South and East China Seas, according to U.S. officials.
It was unclear how seriously Beijing takes the warning.
In February, following Mr. Kerry's visit to Beijing, Chinese leaders told a visiting American delegation that they didn't take U.S. warnings seriously.
"Unfortunately, I don't think they're convinced by our muscularity," said a former administration official who took part in the delegation.
"If we think we're ready to pull the trigger but they don't think that we're ready to pull the trigger, that's when bad things happen."