If the $300 million Clover Hill Farm project becomes reality, it will mark the latest, largest and, perhaps, last major development in Manassas, Virginia's fastest growing city during the early 1980s.

The 382-acre commercial, residential and retail project being proposed by Kettler & Scott, a major Northern Virginia developer, will add about 4,000 residents to the city in its first five years, planners estimate. The current population of Manassas is 20,500.

The City Council is expected to vote on Kettler & Scott's rezoning request, the largest in the city's history, in the next few weeks. In addition, Prince William County supervisors will need to vote on rezoning for about 50 acres of the project that lie within the county. The project has yet to come before the county's Planning Commission.

The developer proposes to build about 1,500 houses and apartments on the property, which has been owned and farmed by the Johnson family for more than 200 years.

The land was sold -- contingent on rezoning approval -- this year to Kettler & Scott, one of more than 20 developers to show interest in the dairy farm. When the bulldozers arrive, a way of life will be plowed under.

"You can fence in the cows, but you can't keep the people out," Joseph B. Johnson, who for most of his 60-plus years has worked the farm with his brother, told an interviewer this year.

Under the developer's proposal, the new residents of Clover Hill Farm will pay up to $250,000 for a detached house, $150,000 for a town house and $120,000 for a condominium -- a far cry from the Civil War-era slave quarters still on the property, which the developer has agreed to preserve, along with a Johnson family cemetery.

The project also includes more than 450,000 square feet of retail and office space, housing for the elderly, a community center, ball fields and child care facilities.

If the project is approved, the developer would expect to break ground in the spring and finish the project in five years.

Little opposition to the project has been voiced, though some planners have expressed concern over its density. One estimate by the city staff is that it will add more than 26,000 car trips per day to the city's already congested roads when the project is completed.

Kettler & Scott has agreed to extend or widen Wellington Road and Hastings Drive, but there is still some concern those concessions will not be enough to handle the additional traffic.

Manassas already has gridlock problems because the county's primary east-west thoroughfares -- Davis Ford Road and Rte. 234 -- dump traffic directly into the city's narrow streets.

The tie-ups have worsened in recent years as Manassas' population has spurted, more than doubling since 1970.

The city's proposed Comprehensive Plan, a road map for future development, termed Manassas' 25 percent growth rate from 1980 to 1985 "phenomenal," noting that Virginia cities of similar size had, on average, posted 7.5 percent increases during the same period.

Manassas' most significant growth occurred during the 1960s, helped by an IBM plant that moved there in 1968. The population went from 3,555 at the beginning of the decade to 9,164 at its close.

During the 1970s, growth was fueled by the linking of Rte. 234 to I-66 and the opening of a local airport.

In 1975, Manassas gained city status and brought in 3,000 more residents through annexation of county territory.

The extension of I-66 to the District, about 25 miles away, and the continued economic growth of Fairfax and Prince William counties have been the catalysts for the city's growth in recent years.

Again IBM played a role: Its employe rolls jumped from 2,777 to 4,946 in 1985. Today about 5,000 work for IBM.

"More and more we are seeing jobs move this way, in all directions from the Washington area," City Manager John Cartwright said.

As the firms have moved in, developers have seen the need for housing for white-collar workers. The average household income was $36,410 in 1985, according to the Comprehensive Plan.

Kettler & Scott senior vice president Richard W. Hausler said: "We saw a maturing transportation system that includes the possibility of commuter rail, the Rte. 234 bypass and the city's own road improvement plan.

"The city of Manassas will be an outstanding residential community. It offers a small-town way of life, and orbits a major employer, Washington, and is only about 10 miles from Dulles International Airport," a booming industrial area.

"For each million square feet of office space, we estimate that translates into 4,000 jobs," Hausler said. "Those people . . . will have to sleep somewhere."

Hausler and his firm also are betting that the nearby Gainesville district and the area around Manassas Airport will become secondary employment sites.

The potential is not lost on developers such as Hausler. "Three or four years ago in Centreville, when we built Sully Station, people had a view of it as an off-site area," he said. "Now, because of the westward movement of employment, people . . . think of it as a good residential community -- period. We think that will happen in Manassas."