As the summit of Southeast Asian nations came to a close, the original proponent of a regional free-trade area said he would return home to fight for a much faster tariff reduction schedule than the group agreed on.

Heads of state of the Association of South East Asian Nations - made up of Indonesia, Malaysia, the Philippines, Singapore and Thailand - formally endorsed Tuesday a plan to enact a free-trade agreement in 15 years.But Anand Panyarachun, Thailand's Prime Minister who originally proposed the Asean free-trade concept and who has pushed for faster enactment of the tariff-reduction plan, said he would try to enact the plan much faster in his own country.

"On our part when I return to Bangkok tomorrow, I shall take the necessary steps to bring down our tariffs," he told the audience at the closing ceremony. He said the maximum rate for all manufactured products coming into Thailand from other Asean countries would be no more than 30 percent by Jan. 1, 1993 and no more than 20 percent by Jan. 1, 1994.

These compare with tariff rate targets of 20 percent for Asean as a whole by 2001. In spite of having proposed the free-trade area idea, Thailand has the highest average tariff rate of the six countries at 32 percent. This is followed by the Philippines at 28 percent.

Meanwhile, in a conference for reporters after the official close, Malaysia's Minister of Trade Rafidah Aziz said Malaysia will offer 3,717 manufactured products and 295 processed agricultural products for inclusion in the zero to 5 percent tariff category and 121 manufactured products and 586 processed agricultural products for reduction to the 20 percent level by Jan. 1, 1993.

At the Asean summit, the group failed to reach a workable consensus on Malaysia's proposal for an East Asia Economic Caucus. The EAEC, which has been strongly criticized by the United States as too exclusive, is a proposed collective of countries organized to fight protectionism in other parts of the world.

Malaysian Prime Minister Mahathir Mohamad was asked whether the EAEC would

put a wedge between the United States and Japan.

"The wedge is already there. It's not of our making," he said. "The only way to ease that wedge is for the United States to be as competitive as Japan. When they feel as competitive as Japan, they will no longer fear Japan."

Sixty percent of Asean's goods are now manufactured products. Intra-Asean trade was $25.3 billion in 1990, up from $12.9 billion in 1989. But that still pales beside the $268 billion in annual trade between Asean countries and the rest of the world.

Furthermore, the size of the collective Asean economies remains very small compared with other trading regions. Despite having almost the same number of people at about 320 million, Asean's combined $300 billion annual economy is only about 5 percent the size of a combined North America and about 7 percent the size of a combined Europe.