The government plans to ease vehicle import screening procedures to encourage the United States to approve Japan's participation in the Trans-Pacific Partnership, a trade source said Tuesday.

In preparatory TPP talks, the United States has emphasized giving priority to supporting its auto industry and requested Japan to reform its tax system and auto emission regulations to lower nontariff barriers to vehicle imports.

While leaving these U.S. requests pending for the actual TPP talks, the government is considering expanding its special treatment for some imported vehicles to help make it easier for foreign automakers to sell their products in Japan.

Although each imported model takes two to three months to clear safety and other checks on samples, the special treatment system for models subject to an annual import limit can shorten the checking period to one month with checks limited to documentary examination.

The government intends to raise the annual import limit for the special treatment system to 5,000 vehicles from 2,000 at present.

Given the United States' wide auto trade deficit with Japan, the United States is expected to stick to maintaining the present 2.5 percent tariff on passenger car imports and the 25 percent tariff on truck imports at the TPP talks if Japan is allowed to join the talks.

In 2011, Japan's vehicle exports to the United States totaled about 1.4 million against some 14,000 U.S. vehicles imported into Japan.