In the Arnold Arboretum's first plant-hunting expedition to the Far East in 60 years, staff members of the Arboretum brought back hundreds of exotic plant seeds, some of which have already begun to germinate, Dr. Richard E. Weaver, an expedition member at the Arboretum, said yesterday.

Weaver and a co-worker, Dr. Stephen A. Spongberg, spent a month in northern Japan and northern South Korea collecting 505 specimens, several of which represent species very rarely cultivated in the West.

The Arnold Arboretum had not sent an expedition to the Orient since 1918 although it had previously been a leader in botanical explorations in temperate Asia.

The primary purpose of this fall's search was to find ornamentals from northern and colder Oriental regions that would thrive naturally in the rigorous New England climate.

Weaver said he is looking forward to the germination of many more species in the collection which are presently undergoing a special cold treatment to promote sprouting.

Weaver predicted that these new Asian plant species would be particularly interesting to horticultural students and would be valuable contributions to American gardens.

The new seedlings have not been added to the regular collection at the Arboretum but they are open to inspection by the public on request at the Arboretum greenhouses, Weaver said.