Groups of Loudoun County business owners and community activists critical of political extremist Lyndon H. LaRouche Jr. are moving quietly on several fronts to try to reduce his group's presence in the county by arranging the purchase of a large LaRouche group industrial property and the group's eviction from its main offices, sources knowledgeable about the transactions said.

The businessmen's aim is to ease the LaRouche group slowly out of Leesburg, where it has its headquarters and where -- to the embarrassment of many of Leesburg's city leaders -- its several hundred associates constitute a major part of the work force, the sources said.

One tactic, discussed by some business owners and community activists, is to take advantage of the group's financial difficulties by trying to buy LaRouche properties.

"It gets them out of here and down the road," said one Loudoun businessman involved in the discussions. "There's a grand design to get rid of these people."

Another business figure who has worked on the deals added: "My main concern is to get them out of downtown Leesburg."

The local residents involved in the transactions said they hope that, as a result, the LaRouche group will move more of its operations to eastern Loudoun, around Sterling, where it has rented warehouse space for its publishing arm. They hope that this is a first stage to leaving the county completely.

LaRouche group spokeswoman Dana Scanlon said she had no information about the deals.

One transaction in the works is the planned sale by LaRouche's organization of its 10-acre tract of Leesburg industrial park land to a Loudoun business figure.

A LaRouche-affiliated group, Lafayette-Leesburg Limited Partnership, has all but signed a contract to sell its 10 acres in Cardinal Industrial Park, off Rte. 7 just east of downtown Leesburg, to a county developer for about $1.2 million, sources said. The group bought the property in 1984 for $373,000 and began construction of a new headquarters and printing plant, but it stopped two years ago because of financial problems.

A Loudoun business figure knowledgeable about the deal said that those involved are not sympathetic to LaRouche and want to make it clear that they are not bailing him out.

"They want to come out wearing the white hats," said the business figure.

The businessmen want to prevent another real estate transaction like the one that fell apart three months ago after many local residents objected. The complex transaction involved the LaRouche group selling its industrial land, then buying an office building at 20 S. King St. where it rents offices.

Many residents objected to the plan because it would have left the LaRouche group with a permanent presence downtown, and with a profit of $300,000.

After the deal collapsed, the LaRouche associates reached an agreement with the building's owner to buy the property. But the LaRouche associates said in a lawsuit filed last week in Loudoun County Circuit Court that the landlord reneged on the agreement to sell them the office building, settling on another buyer. The lawsuit was filed by the Lafayette-Leesburg group and top LaRouche aide Edward Spannaus against the partnership that owns the building and against its lead partner, Reston lawyer Harold Miller.

The lawsuit asks that the owner be forced to sell the office building to the LaRouche group.

Sources knowledgeable about the transaction confirmed that Miller had found another buyer. Also, the sources said that the LaRouche group has been late in paying its rent on the office space recently. They added that the group almost certainly would be evicted in the event of a sale to someone else.

The LaRouche associates have been denied access to one floor of their offices at 20 S. King for several months, ever since a federal bankruptcy judge declared three LaRouche-affiliated groups in involuntary bankruptcy because of unpaid debts.

The LaRouche associates now are doing much of their research and publishing work in private apartments recently outfitted with computers and telephones, sources said. In addition, the LaRouche group recently has given up its interest in two Virginia farms it once owned. Several months ago it settled a debt to an Arlington law firm by transferring ownership of the 64-acre Sweetwater Farm near Harpers Ferry, W.Va., to the firm, Fensterwald & Alcorn, which has represented the group in criminal cases. The group had acquired the farm in 1984 for $400,000.

Two months ago, the LaRouche group relinquished its share of ownership of a 4,500-acre farm in Pulaski County, 60 miles southwest of Roanoke. The farm had been in serious debt, and in May the LaRouche organization transferred its majority ownership in the $1.7 million farm to its partner, Anthony W. (Dan) Murdock, a retired Army major and civilian intelligence official.

If the planned industrial park sale goes through, it would leave only one property in Loudoun still owned by the LaRouche group -- its bookstore in downtown Leesburg. LaRouche's estate, a 171-acre farm outside of town that is worth at least $1.3 million, is owned by an Oklahoma oilman and LaRouche backer.

In addition, two other farm properties in Loudoun have been bought by a Texas supporter of LaRouche, but the sales had escaped public notice.

Helen Boyce of Baytown, Tex., who ran unsuccessfully for mayor there two years ago on the LaRouche ticket, acquired two rural Loudoun properties in May 1986. The first, 74 acres near Purcellville, is assessed at $323,600, according to county records. The second, 218 acres in the Round Hill area, is assessed at $557,000.

Realty transfer records in Loudoun and in San Antonio show that, 14 months ago, Texas lawyer Frank Adams acquired the two properties from their longtime owners and on the same day he swapped them for a property Boyce owned in Bexar County, near San Antonio, worth about the same amount.

Adams said in an interview last week that at the end of the transactions, Boyce, whom he described as his second cousin, became the owner of the Virginia farms, and he owned her land in Texas.

Boyce said in an interview that she plans to move to the larger of the two Loudoun properties in a few months so she can be near LaRouche headquarters. She added that she will allow LaRouche associates to farm the tracts as LaRouche successes against the background of what LaRouche calls the imminent "collapse" of American farming.

"We want to show how the American farming system can operate," Boyce said.