Traffic around the Johnsons' family farm is so bad that family members have to dodge cars when they walk their cows from one pasture to the next. But if everything goes as they plan, the owners of the 382-acre Clover Hill Farm in Manassas won't have to worry about that problem much longer.

The Johnsons have sold their family farm to Kettler & Scott, a Northern Virginia developer, who is proposing to develop a $300 million residential, commercial and retail project. If approved, the project, called Clover Hill Farm, would be one of the largest rezoning cases in the city's history.

"You can fence in the cows, but you can't keep the people out," said Joseph B. Johnson, 62, who has worked the 150-cow dairy farm with William, his younger brother, for most of his life. "Just within the past four or five years it's gone completely wild around here. We're completely surrounded {by development}."

Johnson and his family, who said they received more than 20 offers from developers to purchase their land, knew their days were numbered as they watched new housing developments gradually surround their farmland over the past 15 years.

Scattered about the land are a number of hay-filled barns and silos shoehorned in between several single-family homes and town house complexes that have been built on neighboring parcels over the years. A slave cabin from the Civil War period and a Johnson family cemetery are also on the grounds. As part of the sales agreement with Kettler & Scott, Johnson said the family has an option to build several single-family homes on the land to replace their existing homes.

The Kettler & Scott project is bounded by Winters Branch, Clover Hill Road, Rte. 234 (Sudley Road) and the Manassas city line.

About 53 acres of the project are located in the county.

The project proposal under review by the county's planning department calls for building 1,273 homes in the city -- mixed single-family detached, town houses and apartments -- and 216 homes in the county. About 10 acres would be set aside for office development and at least 40 acres for restaurants, clothing stores and other retailers. Also proposed are a church, centers for children and the elderly, ball fields and a community center and five miles of jogging trails.

"Our objective, of course, is to knit all of this together with the landscape to make it a real town center for the new community and not just make it another strip center," said Richard W. Hausler, a senior vice president for Kettler & Scott. The company is also developing the 340-acre Sully Station and the 370-acre Sully Station Phase II in Centreville.

Realizing that the new development will add people and traffic to the area, Hausler said Kettler & Scott has included several key road improvements in the project. The company is offering to pay for extending and widening Wellington Road through the development to Richmond Avenue and extending Hastings Drive along the city line to connect with Hastings Street in the city.

The roads would be built first. Afterward, construction of the residential and commercial portions of the project would begin at the same time, Hausler said. Once started, construction of the entire project would take about seven years.

"Our approach with significant zoning changes like the ones in this project is to spend a lot of time in the living rooms of residents talking to them," Hausler said. "We want to bring in quality development that's an impressive addition to the area and good for property values in the area."

William Shelly, head of the city's planning department, said he could not say when the department would turn the plans over to the planning and zoning commission, which would also review the plans and schedule a public hearing.

"This is one of the more significant rezoning applications we've ever had because of the mixture," he said. "We don't anticipate any opposition {to the plan}."

The land is now zoned for agricultural use and would be rezoned to a combination of residential and commercial uses, which would be "somewhat consistent" with the city's comprehensive plan, Shelly said. According to the plans submitted to the county, much of the office and retail development would be constructed along Rte. 234. Most of the multifamily housing and the town houses would be built along Wellington Road while many of the single-family detached homes would be located off Clover Hill Road and Hastings Drive.

The development in the southwestern secton of Manassas, where Clover Hill Farm is located, is part of the building boom in the entire county. Ryan Homes' Jackson Manor, Richmond American's Lee Manor, Woodside Homes' Cloverhill Edition and Markay Builders' Winter's Ridge are among the major new home projects around the Clover Hill farmland.

According to the Prince William economic development office, there are 46 projects for offices, hotels, restaurants shops and resort areas planned or under construction on more than 5,000 acres in the county. Several major residential and commercial projects are already underway in Manassas, including Bull Run, a 100-plus acre office/residential development, Manassas Office and Research Park, a 25-acre project near the International Business Machines facility and Linden, a 192-acre mixed-use project.

"Manassas has been growing pretty consistently since the 1960s," Shelly said. "The growth in this area is continuing to keep up with the rapid pace in the area."

The city's 1982 comprehensive master plan is now being revised by county officials as part of their effort to adapt to the rapid movement of developers, builders and people to the city and the county. Water and sewer facilities are already in place in the Clover Hill Farm area, which has helped attract the interest of major national and local developers and builders.

One indicator of the potential success of Kettler & Scott's Clover Hill Farms project is that new homes in the area are selling well. At Ryan Homes' Jackson Manor project, 10 of the 50 lots sold before a model was opened. Construction for the 1 1/4-acre homes is just beginning and they are expected to cost between $117,900 to $133,900. At Richmond American's Lee Manor project, 50 of 155 single-family homes, which cost between $131,000 and $157,000, have been sold since May 1986.

"They {the buyers} like the country-type lifestyle, the peacefulness," said Kris M. Lancaster, the project's sales manager.

Ryan Homes' Bobbie Hart said, "Everything is so built up in Fairfax and prices so exorbitant that people are coming out here and getting a little bit more house for their money."

As far as Joseph Johnson is concerned, the more people move to the area, the harder it will be to find someone living on land they have owned for more than two centuries. Said Johnson, "There's not going to be much farmland left much longer."