Atlantic Research Corp., the Alexandria defense contractor that fended off a hostile suitor earlier this year, yesterday faced the prospect of a new bid involving not only the previous bidder but other stockholders as well.

Halcyon Investments, a firm led by New York investor Alan B. Slifka, said yesterday it plans to seek meetings with at least two other major Atlantic shareholders to discuss "on an exploratory basis, whether or not any ... act, arrangement, understanding or relationship would be beneficial," according to a filing Halcyon made with the Securities and Exchange Commission. The other shareholders include Clabir Corp., which had unsuccessfully sought to take over Atlantic earlier this year.

May O'Leary, a stock analyst with the Richmond firm of Baker & Watts, said the announcement could be an effort to find a new buyer for Atlantic. "It puts the company back into the takeover spotlight," she said.

Slifka refused to elaborate on his plans yesterday. William H. Borten, Atlantic's president, also declined comment but repeated the firm's long-stated desire for independence.

In over-the-counter trading yesterday, Atlantic closed at $26.75, up $1.25.

The three shareholders mentioned in Halcyon's statement together own about 23.9 percent of the company's stock, worth nearly $59 million. The largest block, 12.4 percent, is held by Clabir., Halcyon, which speculated on Clabir's bid, owns about 5.5 percent.

Halcyon also said it recently was contacted by a third investor "who claims ownership of or control over slightly less than 5 percent of the company's common stock." The filing did not identify the third investor. Borten said yesterday he does not know who the investor is.

According to Halcyon's statement, Slifka and other Halcyon officials met with Borten and another Atlantic representative on Sept. 16. The statement said they discussed Halcyon's investment in Atlantic, as well as the company's history and future.

"Mr. Borten invited Halcyon to meet with the company's investment bankers," the statement continued. "No agreements or understandings were reached between Halcyon and the company."

Borten downplayed the meeting, saying it was little more than a courtesy during a New York business trip.

Slifka's flurry of activity appears to result from Clabir's failed bid for Atlantic. Atlantic aggressively fought the bid and Clabir, which owns the General Defense Corp., lacked the financing to fight back. "Everybody knows Clabir doesn't have the financial resources to take over the company," said O'Leary.

One source familiar with the recent discussions noted that Slifka lost money on the Clabir takeover attempt, buying 510,400 shares at an average price of $32, about $7 to $8 more than recent market price. His attempt to coordinate activity among the three investors seems primarily an effort to recoup his loss, this source said