Gov. John N. Dalton dedicated the $115 million Bear Island Paper Company Newsprint Mill in Hanover County, Va., yesterday at a ceremony attended by about 350 local officials and industry leaders.

Newsprint production started at the facility in December, 15 months after construction on the plant began. Dalton and Peter M. Brant, Bear Island Paper Company president, had marked the beginning of construction jointly in September 1978 by driving "golden" railroad spikes at the site at Doswell, off Route 738 and east of Interstate 95.

Dalton personally had solicited the plant for Virginia, and it now employs about 230 maintenance, production and service personnel. In addition, the company estimates it has created another 1,000 jobs in the local market.

The company has a local payroll of $5252,000 a month, and it buys about $3.6 million of parts, wood, electricity and other goods and services from local businesses each month, it said.

The compnay is a joint venture of The Washington Post Company, and Brant-Allen Industries Inc. of Greenwich, Conn., a subsidiary of the Bato Company Inc.

The Washington Post and The Wall Street Journal, owned by Dow Jones, are two big customers of Bear Island. Katharine Graham, chairman of the board of The Washington Post Company, and Warren Phillips, chairman of Dow Jones, attended yesterday's dedication.

The newsprint mill, which runs 24 hours a day, is the first to use only a thermomechanical process, involving grinding and steam pressure, rather than a chemical cooking process which produces the strong smells usually associated with pulp and paper mills.

The mill is designed to produce 500 tons of newsprint a day, requiring about 175,000 cords of Southern Pine a year. At full production the plant would use an estimated 1.5 million gallons of water a day.