Negotiations on the Trans-Pacific Partnership remain strenuous as countries seek to protect feeble domestic industries, but the framework will have a major impact on the global economy once finalized, Ira Shapiro, a former general counsel to the Office of the U.S. Trade Representative, said on Thursday in Tokyo.

"(The) talks have been handled constructively, and I am hopeful we can get a good outcome" since TPP is the most important free trade agreement in the past 20 years, Shapiro, the chief trade negotiator under the Clinton administration, said during a speech at the Japan National Press Club.

"From what I hear, Japan's negotiation team is participating constructively" in the negotiations, he added.

Following its decision to join the TPP talks in March, Prime Minister Shinzo Abe's government has been haggling over trade tariffs with the 11 other members with a view to hammering out the final framework by yearend.

But the talks are reportedly being delayed as members refuse to yield ground on key fields. Japan, for example, has been battling to save its farmers from brutal competition should all import tariffs be eliminated as per the TPP's overriding principle, while the United States is seeking to protect its automobile industry.

Shapiro, who was in charge of settling automobile trade disputes between Washington and Tokyo in the 1990s, said he remains optimistic.

"Each country has their sensitive sectors and political difficulties," Shapiro acknowledged, adding that negotiations on the auto trade are "always controversial" because two-thirds of the U.S. trade deficit with Japan comes from the automobile industry.

But agreements reached in the 1990s that resulted in Japanese makers building more cars in the United States have changed the position, Shapiro said. Such developments "will make it possible to handle the topic," he said.