The Manassas City Council approved rezoning last night for the $300 million Clover Hill commercial and residential development to be built on a 334-acre tract that is now the city's last working farm.

The unanimous vote on the project, largest in the city's history, came after little discussion. A second vote must still be taken, but is considered a formality.

Clover Hill, planned by Kettler & Scott, a major Northern Virginia developer, is expected to add about 4,000 residents to the city of 20,500 over five years. Manassas, about 25 miles southwest of Washington, has more than doubled its population since 1970.

The developer plans to build 1,500 houses and apartments on what is now a dairy farm. Site plans also call for more than 450,000 square feet of retail and office space, housing for the elderly, and recreational and child care facilities. Sale of the property was contingent on the rezoning.

The Johnson family has owned and farmed the land for more than 200 years, and Joseph Johnson, 63, who was born there and has worked on the farm all of his life, said yesterday: "I think it's going to be a good development for the city of Manassas. But I'm sorry to see it cease to be a farm. There comes a time when crops mature and land develops. From what has happened around us, it was difficult to run a farm."

The project drew little opposition.

When completed, the project is expected to add about 26,000 car trips a day to the city's road system, but Kettler & Scott agreed to make road improvements and street extensions that the developer says will compensate for the traffic increase. Planners have expressed some concern that the road work will not be enough to handle the new traffic.

Manassas already has significant traffic problems, created because Prince William County's two primary east-west throroughfares -- Rte. 234 and Davis Ford Road -- funnel traffic onto the city's narrow streets.

The Prince William Board of County Supervisors will vote on rezoning for 50 acres of the project that lies within the county. Under city law, Kettler & Scott will also have to get each subdivision plan approved.