G.M. Holdens, the Australian subsidiary of General Motors Corp., expects to increase exports this year to record levels.

GM's exports from Australia include:* Motor engines to Britain, South Korea, Thailand, West Germany and the United States, and engine castings to West Germany.

* Brake discs and other components, sent to Vauxhall Motors Ltd. in the United Kingdom.

* Complete cars and kits for assembly shipped to Papua New Guinea, New Zealand and Southeast Asian countries such as Thailand, Indonesia and Singapore.

Company executives believe that exports to Japan are not far away.

The GM Australian subsidiary is already the country's largest exporter of manufactured goods.

Exports last year grossed nearly US$170 million, up from $150 million the previous year. This year exports could be at least $250 million, the company said.

Overseas shipments have benefited from a favorable currency exchange rate, a large investment in new facilities, a greater emphasis on quality control and an extensive reorganization of operations.

The most successful export product is the GM two-liter four-cylinder Family Two engine. Some 1,000 of these engines are exported each working day to Adam Opel AG, of West Germany and Vauxhall in the United Kingdom.

In February the company celebrated the dispatch of the millionth engine for export, seven years after the first engine rolled off the production line of GM's Fishermens Bend plant in the southern city of Melbourne.

A GM spokesman said the engine showing potential for the company is the new fuel-injected V8 that was exhibited in Detroit earlier this year. Between 30,000 and 40,000 of these engines could be exported each year to the United States, he said.

The Australian plant is also producing a V6 engine, which has prompted supply inquiries from Europe.

We have considerable expertise in producing low volume engines at a competitive price. We have identified a large number of niche engine opportunities and see our growth coming from there, said GM Australia's Peter Thomas, engine division managing director.

The company recently announced that it expected to more than double its vehicle market share in Asia this year through the introduction of the Australian-made Commodore model in Thailand.

About 600 of these vehicles will be shipped for assembly in Thailand during 1988, along with 900 units of the Australian-made Camira model.

Thailand this year will become the company's second-largest export market after New Zealand.

Late last year GM announced the merger of the bulk of its Australian operations with Toyota's Australian operations. The U.S.-Japanese new joint venture is expected to become a dominant operator in Australia, with the potential to capture no less than 40 percent of the Australian market.

The merging of operations springs from the Australian government's 1984 auto industry plan to reduce the number of car manufacturers in the country to three from five, and to reduce the range of locally made models from 13 to a maximum of six.

Other auto manufacturers in Australia are Ford Motor Co., Nissan Motor Co. and Mitsubishi Corp.