By David Brunnstrom and Matt Spetalnick

WASHINGTON (Reuters) - An international ruling next month is expected to deprive China of any legal basis for its claim to most of the South China Sea, and Beijing risks being seen as an “outlaw state” unless it respects the outcome, the Philippines’ chief lawyer in the case said on Wednesday.

In an interview with Reuters, veteran Washington attorney Paul Reichler expressed confidence that the Permanent Court of Arbitration, based in The Hague, would rule in Manila’s favor on July 12 in a highly charged case against Beijing, which rejects the tribunal’s jurisdiction and says it will ignore the ruling.

The Philippines, a close U.S. ally, is contesting China's historical claim to about 90 percent of the South China Sea, one of the world's busiest shipping lanes. Several Southeast Asian states have overlapping claims in the sea, and the dispute has sparked concerns of a military confrontation that could disrupt global trade.

Reichler, who heads Manila’s legal team in the 3-1/2-year-old case, said he was not privy to the ruling and did not expect to be informed until the last minute. But he had little doubt that Manila would win the legal argument, matching the consensus in Washington and most major foreign capitals.

“We are confident we will have success on the merits,” said Reichler, who called the case potentially one of the most far-reaching to be decided by the court. He spoke just hours after the court announced the date for its ruling.

China bases its South China Sea claim on a "Nine Dash line" stretching deep into the maritime heart of Southeast Asia and covering hundreds of disputed islands and reefs, rich fishing grounds and oil and gas deposits.

Reichler said a ruling against Beijing “would deprive China of any legal basis for making such a claim.” Manila argues that China's claim violates the U.N. Convention on the Law of the Sea and restricts its rights to exploit resources and fishing areas within its exclusive economic zone.

On Wednesday, China said Manila's approach flouted international law and Beijing would not accept any third-party decision on the issue.

Reichler said for China to reject the ruling meant it had "essentially declared themselves an outlaw state" that did not respect the rule of law.

Reichler is an international lawyer with a reputation for representing small countries against big powers, including a 1980s case by Nicaragua that accused the United States of funding right-wing Contra rebels against a left-wing government.

Amid rising tensions in the South China Sea, Reichler said “nobody wants or should even contemplate the use of force.”

He predicted China would face pressure to abide by the ruling from other rival claimants, including Vietnam, Indonesia and Malaysia, despite signs that some other Southeast Asian countries are wavering in response to U.S. efforts to forge a unified regional front.

“It may be that in time ... the Chinese will come to realize that they have more to lose than to gain from creating a chaotic, lawless situation,” he said.

China has accused the United States of "hyping" the dispute and has warned that complaints would snap back on its critics. But it has largely avoided specific threats of how it might respond to the ruling.

U.S. officials are worried China may declare an air defense identification zone in the South China Sea, as it did in the East China Sea in 2013, and by stepping up its building and fortification of artificial islands.

They say the U.S. response to such moves could include accelerated "freedom-of-navigation" patrols by U.S. warships and overflights by U.S. aircraft as well as increased defense aid to regional countries.

(Editing by Leslie Adler)