Abe will send legislation to parliament next month - with the backing of his coalition partners virtually assuring its passage - allowing Japan to ship fuel and ammunition to American units anywhere, should Tokyo judge its national security to be at stake.
Japan and the United States have no territorial claims in the energy-rich South China Sea, but tensions are rising between China and Philippines in the strategic waterway, where some $5 trillion in ship-borne trade passes every year, much of it heading to and from Japanese ports.
Washington is treaty-bound to defend Manila if it is attacked.
"If the Philippines were to clash with China, they would send an SOS to their ally the US," said a policy expert in Japan's Liberal Democratic Party. "If the US military were then to seek assistance from the Self Defense Forces, the question then becomes what Japan can do."
As part of a raft of bills to reform the country's security strategy, the parties in Abe's coalition have agreed to drop a restriction that has allowed Japan to provide ally the United States with logistical support only in "areas around Japan" - code for a conflict with North Korea.
Policymakers have avoided saying what areas would now be open for Japan's rearguard support, but three government officials and a ruling party lawmaker told Reuters the bills open up islands claimed by China and the Philippines as a possible future theater of operations for Japan's Self Defense Forces.
Japan's potential non-combat involvement in the flashpoint of the South China Sea, providing logistical support to an American defense of the Philippines, will likely stir debate in coming months over what has so far been Abe's geographically vague push for a more assertive military, one official said.
In two years in office, Abe has eased curbs on arms exports, reinterpreted the pacifist constitution to allow Japan to defend friendly countries under attack and taken a more assertive diplomatic stance.
Uncertainty over applicability of law
Japan's military has offered logistical support abroad before, such as fuelling allied ships in the India Ocean on their way to Afghanistan. But those cases required a new law each time. The new laws remove that requirement, although the government will still need parliamentary approval for new operations.
Japanese Defense Ministry spokesman Hirofumi Takeda said it was impossible to "debate in advance whether a specific situation is applicable" under the planned laws.
"A judgment would be made, depending on the specific and concrete circumstances, as to whether it qualifies as 'a situation having a grave impact'" on Japan, as required under the plans.
Security expert Takashi Kawakami at Takushoku University says the possibility of an unforeseen clash between the Philippines and China is rising in the South China Sea.
"The Philippines will get more assertive if they think America's expanded deterrence is at work," Kawakami said. "And China may take a hard line out of consideration for domestic circumstances."
As China creates a series of artificial islands by reclaiming land around seven reefs in the Spratly islands also claimed by the Philippines and Vietnam, Manila in recent days has sought more "substantive" support from Washington.
US President Barack Obama has expressed concern that China is using its "sheer size and muscle" to push around smaller nations in the disputed sea, drawing a swift rebuke from Beijing.
Dennis Blair, former commander in chief of the US Pacific Command, played down the chances of conflict between China and Philippines. In the event of an escalation, an air and maritime exclusion zone would likely be established in the area while diplomatic negotiations were carried out, he added.
The White House did not provide immediate comment.
A senior Philippine military official familiar with US Pacific Command operation said Manila would welcome any efforts by Tokyo to extend its maritime operations in the disputed areas in the South China Sea, especially in assisting the US forces.
"Since the US and Japan have an agreement, I would not be surprised if Japan is dragged into a conflict in the South China Sea," said the official, as US and Philippine forces began their biggest combined military exercise in 15 years.
The USS George Washington (CVN-73) conducts a replenishment-at-sea with dry cargo ship USNS Charles Drew (T-AKE-10).