By Greg Torode
HONG KONG (Reuters) - The Philippines' legal challenge against China's claims in the South China Sea is gathering pace, emerging as a "proxy battle" over Beijing's territorial reach.
Manila has assembled a crack international legal team to fight its unprecedented arbitration case under the United Nations' Convention on the Law of the Sea - ignoring growing pressure from Beijing to scrap the action.
Any result will be unenforceable, legal experts say, but will carry considerable moral and political weight.
The Philippines has invested a "huge amount of political capital in this legal gambit and it wants to ensure success regardless of the cost," said security scholar Ian Storey of Singapore's Institute of South East Asian Studies.
"If the Philippine team submits a less than convincing case...this would be very embarrassing for Manila and put it right back to square one in its dispute with China.
"Beijing would also be emboldened to pursue its claims even more assertively than it has been doing over the past few years."
Beyond the legal questions, the case carries political and diplomatic risks and is being closely watched by Japan and Vietnam, locked in their own disputes with China over sea territory, officials from both countries say.
The United States, which is deepening military ties with the Philippines, a longstanding treaty ally, is also watching.
The legal battle mirrors tensions at sea, where China and the Philippines eye each other over rival occupations of the Scarborough and Second Thomas shoals.
Chinese vessels occupied Scarborough after a tense two-month standoff between rival vessels last year - a move some regional analysts have described as an effective annexation by Beijing.
The Philippines accused China of further encroachment when a naval frigate and two other ships steamed within five nautical miles of a dilapidated transport ship that Manila ran aground on Second Thomas Shoal in 1999 to mark its territory.
One Asian envoy from a non-claimant country said: "We are watching and worrying about an accident or miscalculation sparking an armed confrontation. So in some ways this growing legal fight looks like the proxy battle, you could say."
Overlapping claims in the South China Sea - traversed by half the world's shipping tonnage - are one of the region's biggest flashpoints amid China's military build-up and the U.S. strategic "pivot" back to Asia.
The claims of the Philippines, Vietnam, Malaysia and Brunei are bisected by China's "nine-dash line" - the historic claim that reaches deep into the maritime heart of Southeast Asia.
European states, Russia, India and South Korea are also monitoring events, given the sea's shipping lanes and potential oil and gas resources, diplomats and military officials say.
Frustrated by slow progress by the Association of South East Asian Nations in easing tensions and fearing its sovereignty was threatened, Philippines officials said they had no alternative.
Unable to contest actual sovereignty in international courts without China's consent, Manila instead launched its arbitration in January - despite formal objections from Beijing.
Philippines Foreign Ministry spokesman Raul Hernandez told Reuters this week that Manila remained positive that the action would clarify the claims and entitlements of claimants to "benefit the region and the international community as a whole".
Manila's team is preparing arguments to show that the nine-dash line claim is invalid under of the Law of the Sea. They are also seeking clarifications of the territorial limits, under the law, of rocks and shoals such as Scarborough - all part of a bid to confirm the Philippines' rights within its 200-nautical-mile exclusive economic zone.
Philippines' lead counsel Paul Reichler, a Washington-based lawyer with Foley Hoag, told Reuters that his five-strong team included British law professors Philippe Sands and Alan Boyle as well as Bernard Oxman from the University of Miami's law school.
Independent legal experts have described the team, managed by the Philippines' Solicitor General Francis Jardeleza, as "formidable", with deep experience of the arcane world of the Law of the Sea, a landmark document approved in the early 1980s.
China has refused to participate, saying the case has "no legal grounds", and is widely expected to reject any outcome its does not agree with.
Foreign Ministry spokesman Hong Lei said China views the move as a breach of a 2002 declaration between China and ASEAN.
"The Philippines has illegally occupied the reefs and islands in the South China Sea that belong to China...China has consistently advocated for resolution to the dispute at hand through bilateral dialogue," he said.
Behind the scenes, Chinese diplomats are telling the Philippines' ASEAN peers that the case has no merit, according to diplomats from the 10-nation grouping.
Philippines Foreign Ministry officials said Beijing demanded that Manila scrap the case as a condition for a long-planned trip by President Benigno Aquino to a regional trade show in southern China this month. Chinese officials said no invitation was ever offered. The trip never happened.
The Philippines' effort, however, was recently given a boost by a decision from an arbitration panel created to hear the case under the U.N.'s International Tribunal of the Law of the Sea.
The five international judges said the Philippines had until March 30, 2014 to produce written arguments about the case's admissibility and merits. China is a member of the tribunal but has forgone its right to select one of the judges to the panel.
Maritime scholar Clive Schofield said the request for the Philippines to provide arguments was potentially favorable. It also meant the case might take less than the three to four years anticipated by Manila when it was launched in January.
"It suggests that the Philippines will be able to present its arguments on the merits of the case as soon as the jurisdictional hurdle is overcome...If I was sitting the Philippines' chair right now I would be happier than sitting in China's," said Schofield, a professor at the University of Wollongong in Australia.
Schofield described the panel as "irreproachable. These guys are at the very top of their game and I expect it would be very unlikely they would be swayed by political issues."
He said that it appeared the panel would not be hostile to China even though it was not contesting the arbitration.
Ultimately, the Philippines was anticipating a "good return" on its investment, said Storey, the Singapore-based expert. A favorable ruling would give Manila confidence in developing oil and gas reserves in disputed areas such as the Reed Bank.
"Foreign energy companies would also feel more comfortable about investing in areas...that lie within the Philippines' exclusive economic zone," he said.
(Additional reporting by Rosemarie Francisco in Manila and Megha Rajagopalan in Beijing. Editing by Ron Popeski)