In a bid to meet fast-rising demand for export movement, Thoresen Thai Agencies PLC is looking to the stock market to help it expand its fleet.

The company recently announced plans to add 10 ships over nine months, bringing its fleet to 18. The plans are based on positive economic data for the shipping and transport industry in recent years, said Chairman Chandram Chandratat.Growth in the sector has been 2.8 percent a year over the past seven years, as international trade has taken an increasing share of gross domestic product. The overall shipping and transport industry is expected to grow 3 percent a year, but growth is expected to be substantially higher in Southeast Asia.

''The increase reflects Thailand's economic growth and attractive investment climate and underlines the need to expand the country's cargo- shipping services to keep pace with demand," Mr. Chandram said.

Thoresen Thai this month launched its initial public offer on the local stock exchange - 9 million shares at a par value of 88 baht ($3.60). Trading is expected to begin in September.

The company hopes to raise 792 million baht from the issue. Much of this is expected to fund the additional vessels, valued at 700 million baht.

"Global demand for ocean freight services using 10,000-to-23,000- deadweight-ton ships is expected to rise between 1995 and 2000," Mr. Chandram said.

The new vessels will not be operated with fixed routes. The market for such tramp services is promising, Mr. Chandram said, adding that he expects at least three firm years.

"Not only will the company's acquisition of an additional 10 cargo vessels improve its performance, but the purchases will also enhance the potential of Thailand's ocean-going shipping industry and keep the trade deficit in balance," he said.

Officials are calling for more efforts to upgrade the domestic fleet. Some 90 percent of Thailand's seaborne trade depends on foreign shipping, contributing to a deficit in service trade estimated at 100 billion baht a year.

While the amount of freight has been rising in recent years to around 84 million metric tons annually, Thai carriers' share is down to around 9.5 percent.

Thoresen Thai is one of the country's oldest shipping companies, with vessels principally serving routes between Thailand and South Korea via Japan and between Thailand and the Middle East and Persian Gulf.

On the north Asian route, it carries largely gypsum, corn, steel, machinery and general cargo. To the Gulf region, its cargo is chiefly rice, sugar, and

machinery and other equipment.

In listing on the local bourse, Thoresen will be joining Jutha Maritime PLC, Regional Container Lines PLC, Unithai Lines PLC and Precious Shipping Lines PLC.

Some of Thailand's industrial conglomerates are moving to establishing their own merchant-shipping operations as a way to contain rising costs. In this category are agro-industrial company CP Group and steel and industrial developer Sahaviriya Group.