WASHINGTON — The Obama administration began a broad effort Wednesday to enlist China to help rein in North Korea in the wake of its deadly attack Tuesday on South Korea.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, urged China to act, calling Beijing "absolutely critical" to the international effort to get North Korea to stop its military provocations.

"It's very important for China to lead," Mullen said Wednesday on the ABC program "The View." "The one country that has influence in Pyongyang is China."

President Barack Obama was preparing to make a telephone plea to President Hu Jintao of China, White House officials said. They added that Secretary of State Hillary Rodham Clinton would likely be calling China's foreign minister, Yang Jiechi, to follow up on similar calls from other senior U.S. officials to their Chinese counterparts.

But few analysts expect China, wary of destabilizing the North, its unpredictable neighbor, to employ its economic and military leverage in any substantial way to try to alter North Korea's behavior. And in Seoul, the South Korean government was left struggling to find the right response, as President Lee Myung-bak found himself with no clear way to proceed despite his past vows to take a hard line against the North.

Lee spent Wednesday conferring with generals and talking on the phone with world leaders like Obama, who offered him their sympathy and support over the artillery attack Tuesday on a South Korean island, the latest in a series of provocations by the North.

Lee's government also traded threats with the North, warning of heavy retaliation should North Korea attack again, while the North warned against even the slightest incursions into its territory.

But despite the strong words, South Korea is showing few signs of actually planning a more forceful retaliation for the attack on Yeonpyeong Island, in which two civilians and two marines were killed. While the South placed its armed forces on high alert and sent F-15 fighter jets to the area, its only military response so far came during the attack itself, when marines on the island returned fire at North Korean positions.

On Thursday, the South's government ordered the deployment of extra troops on islands near the disputed border with North Korea, Reuters reported

On Wednesday, during an emergency session of the National Assembly, South Korea's legislature, right-wing lawmakers called for bolder military action in response to the island's shelling. They also criticized Lee for not retaliating immediately with greater force.

Although China has in the past tried to influence North Korea, it has been reluctant to do so in recent months. The reason in part, analysts say, is that Beijing does not want to destabilize the North when it is in the middle of a succession process brought on by the illness of its leader, Kim Jong Il, who is believed to be making way for one of his sons, Kim Jong Un, to take over.

Obama's decision to accelerate the deployment of a U.S. aircraft carrier group to the region is intended to prod the Chinese.