The arms industry of this city-state, flushed with what is considered here a successful introduction of its wares at a Marine Corps exhibit in Quantico two months ago, is planning a return U.S. visit with more new products.

This week, six government-owned companies in the fields of high technology and arms manufacturing pooled their skills to form the Singapore Technology Corp.

One of the firms, Chartered Industries of Singapore, sells to armies in the Middle East, Africa, Thailand, South Korea, West Germany, Australia and New Zealand. Three thousand of its latest lightweight rifles have been supplied to resistance forces in Cambodia under Son Sann.

The Singaporean government may be following the recommendations of arms experts in the United States to look to Central America for more sales. Among the wares promoted at this week's inaugural ceremony for the new corporation were a lightweight, low-cost machine gun to be used in assault, defense and antiaircraft combat, a two-gun aircraft pod, and a 60-mm mortar.

None of these weapons would represent new technology for U.S. forces, although the mortar is said to be smaller and more portable than any others and "might come in handy in Central America," according to a diplomatic source.

The Singaporeans were disappointed that they were not able to market their Ultimax 100 machine gun in time to compete with a Belgian model for a 1980 U.S. Army contract. Belgium is to deliver 35,000 guns.

The U.S. Marines are thought by experts here to favor Singapore's Ultimax 100 over the Belgian Minimi, and the Singaporeans still appear to be pitching.

"If we can get someone in the U.S. forces to use it, that would be a feather in our cap to show other potential purchasers," said a Singapore arms industry source.

The next two venues for the Singaporeans will be another Marine exhibition and an Association of the U.S. Army show.

They probably will add to their wares an extended-range mortar bomb now in production, small-arms ammunition, mines, grenades, grenade launchers and tank ammunition.

The government is projecting annual sales of more than $25 million for the rifles and machine guns annually.