Hagel plans to call for restraint in the disputed South China Sea and to underscore America's focus on Asia-Pacific at the gathering in Brunei of defence ministers from the Association of Southeast Asian Nations, China and elsewhere, officials said.
The two-day ASEAN meeting is the main event of Hagel's week-long trip to Southeast Asia but a mounting crisis between Syria and the West has repeatedly competed for his attention.
"We are ready to go, like that," Hagel told the BBC in an interview Tuesday, when asked about potential military action against Syria.
The confrontation over the Syrian regime's alleged use of chemical weapons has illustrated the challenge facing Washington's much-touted "rebalance" towards the Asia-Pacific.
Turmoil in the Middle East has repeatedly overshadowed the bid by President Barack Obama's administration to bolster trade and military ties with economically vital Asia.
Despite Pentagon budget cuts, US officials say Washington will stick by plans to deploy more ships, troops, training and hardware to countries anxious about China's growing military reach.
Hagel met Wednesday with Japan's defence minister, Itsuno Onodera, who thanked him for attending the gathering despite the Syria situation.
Onodera said this week that Japan could be a "main player" if conflict erupts in Asia and needed to be wary of China's maritime ambitions.
Tokyo is feuding with Beijing over territorial claims in the East China Sea while some Southeast Asian countries have accused China of increasingly provocative acts in asserting its claims to nearly all of the South China Sea.
Such strains are expected to be a key focus of the talks and to feature in Hagel's discussions with his counterparts from South Korea, Vietnam and Brunei.
Hagel is also due to meet China's defence minister, General Chang Wanquan, and Myanmar's defence chief on the sidelines of the ASEAN conference.
The United States has avoided taking a position on individual disputes but Hagel reiterated calls for the adoption of a South China Sea code of conduct to prevent potential clashes.
China has been accused of dragging its feet on the issue, but this year said it would enter into future talks with ASEAN on the issue.
The Pentagon is offering ships, radar and other security assistance to countries in Southeast Asia, partly as a counterbalance to China's military build-up.
On Tuesday, Hagel announced the sale of eight Apache helicopters to Indonesia during a visit to Jakarta.
Hagel, however, has trodden carefully when discussing China during the trip, and officials said Washington wanted to avoid inflaming tensions.
"This is not about encircling China or anybody else," the US Defense Secretary said in the BBC interview.
"This is about economic interests, it's about the world, it's about prosperity, stability and security."
Hagel acknowledged disagreements with China over cyber security -- Washington has blamed Beijing for extensive digital espionage against American industry and government agencies.
Ties have also been strained over allegations by US whistle-blower Edward Snowden of American spying and hacking activities directed at China.
"Yes, we have differences, but the only way to get through those differences is to work through them," Hagel said.
Hagel is expected to discuss the threat posed by North Korea's nuclear weapons and missile programme with his counterparts.
North Korean sabre-rattling has eased in recent months but Hagel said the regime must take steps to abandon its nuclear weapons and allow in UN inspectors.
"They've got to come clean, let people come in and inspect," he said.
The ASEAN gathering brings together defence ministers from 10 Southeast Asia countries plus Japan, China, South Korea, the United States, Russia, India, Australia and New Zealand.