Cortes W. Randell, the convicted stock swindler, has won the support of Sen. Edward M. Kennedy (D-Mass.), Virginia Lt. Gov. Charles S. Robb, former attorney general Elliott L. Richardson and assorted other conspicuous neighbors in the McLean area for his latest venture.

Randell, in an effort to find a buyer for his 53-room Tudor mansion and 18 acres of land on the Potomac Palisades, wants to convert the property to a corporate retreat -- a place with overnight accommodations where a company could hold seminars and other meetings for its personnel.

"One of the top corporations in the country is interested in the property," which is on the market for $3.5 million, according to David A. Edwards, executive director of the Fairfax County Economic Development Authority. The authority has been carrying on an aggressive campaign to attract business to the county.

But the McLean Citizens Association of Fairfax County Supervisor Nancy K. Falck (R-Dranesville), who represents the area, claim that Randell is using deceptive tactics to win support.

In an effort to win his neighbor's backing for a county ordinance that would permit the retreat to be created, Randell told them in a letter there were only two choices -- permitting the conversion or subdividing the property into 17 lots for more houses. All but one of the neighbors opted for the retreat.

"That was a very misleading letter," said Mrs. Falck. "What would you do if you were presented with a choice like that? No one wants to see all those houses built there."

Mrs. Falck and the citizens association fear passage of the ordinance could open the door to other such retreats on other large properties along the Potomac River, and thus change the character of the area, whose seclusion and spectacular vantage have attracted the rich and the powerful.

What would prohibit a Playboy Club from being established? It's a corporation," said Mrs. Falck.

Randell served eight months in federal prison in 1975 for his role in a stock fraud involving the National Student Marketing Corp. After he was convicted of 17 more white-collar crimes involving securities and mail fraud, two federal prosecutors, in advocating another jail sentence, wrote: "Randell has contiually shown himself to be a person who will not hesitate to deceive investors, banks and government agencies."

Randell, free on bond, could be sentenced to as long as 105 years in prison and $82,000 in fines if his convictions are upheld on appeal.

Lilla Richards, spokesman for the McLean Citizens Association, recalled the prosecutors' assertion and added: "I believe Mr. Randell is trying not only to deceive government agencies but his neighbors for personal gain."

She said "there is no way in hell he could get 17 houses on that property" because the land would be unable to support all the septic pits or drain fields that would be needed for that kind of development. The Randell property and the adjacent area is not within the sector where Fairfax County permits public sewer.

Mrs. Richards said that if 17 houses can't be built, then lighter development -- perhaps only eight houses or even fewer -- would be preferable to taking a chance on the ordinance that would permit a corporate retreat.

The economic development authority's Edwards said the president of the unnamed corporation that would establish a retreat "has been to the property and said this is what he wants."

The mansion's 53 rooms, which, cover 15,400 square feet, include three large rooms, each of which can seat 200, two dining rooms, including one that can seat 60, two kitchens, a library and "21 rooms suitable for small seminars or overnight accommodations," according to a Randell brochure. There is also an indoor swimming pool, workshop and a small stone outbuilding described in the brochure as a "fun house."

Edwards said officials of the company that wants to establish a retreat will meet with neighbors and other residents before the ordinance proposal goes before the Fairfax Board of Supervisors Jan. 14. "The company does not want a fight," Edwards said. "The bottom line is going to be, if the company is not wanted, it will go away."

The ordinance that would permit the retreat was proposed by Mrs. Falck's predecessor, John P. Shacochis, who acted after the petition of support from Randell's neighbors -- including Kennedy, Robb, Richardson, former Interior secretary Stewart Udall and others.

"I don't think Randell used any deception," he said. "I think he presented what he felt he was entitled to, and that means 17 houses."

According to Supervisor Martha V. Pennino (D-Centreville), vice chairman of the Fairfax board, county staff is still working to tighten the ordinance so that it could not be the basis for a proliferation of corporate retreats.