A national survey of industrial properties shows that the vacancy index declined to 3.5 per cent in December.

The survey of 12 metropolitan areas, made by the Coldwell Banker real estate firm, showed that the supply of vacant industrial space earlier declined from 4.2 per cent in June, 1977, to 3.7 per cent in September.

"Most of the recent decline is due to an increased demand for existing manufacturing buildings, in spite of a slighted increases vacancy rate in warehousing, and distribution space," the report said.

Nationally, the rate ranged from a low of no vacancies in Seattle to 6.3 per cent in Dallas, where several previously used manufacturing and warehouse buildings were placed on the market in recent months.

In the Washington area, the vacancy factor - involving mostly warehouse and light industrial space - held steady at 3.6 per cent from September through the end of the year.

Chicago, Dallas, Kansas City and North-Central California had higher vacancy rates. Portland, Ore., Minneapolis-St. Paul, Houston, Denver and Atlanta had lower vacancy rates than Washington.

The source of the information is the Coldwell Banker industrial properties data bank, a computerized information system that includes data on more than 5o,000 industrial properties of varied sizes in 12 different areas.