Atlantic Research Corp., trying to stave off its second hostile suitor this year, yesterday filed a lawsuit accusing Sequa Corp. of a pattern of "misrepresentations" and fraudulent conduct in connection with Sequa's attempt to take over the company.

In papers filed in federal court in Delaware, ARC charged that Sequa, a New York-based conglomerate, violated federal securities and racketeering laws during a period when it was buying 1.7 million shares of ARC stock and making a $275 million cash tender offer for the Alexandria company.

At the same time, ARC, a rocket propulsion manufacturer that has become one of the Washington area's largest defense contractors, urged its shareholders to reject Sequa's $30 a share tender offer as inadequate. The company also instituted a so-called "golden parachute" provision for its president, William H. Borten, and its two other top executives, guaranteeing them a payment equal to twice their annual salaries and bonuses if any outsider buys the company.

A Sequa spokeswoman said the company would have no comment yesterday. Sequa, until recently known as Sun Chemical Corp., is a $1.2 billion conglomerate with diverse interests that include gas turbines, jet engines, military electronics, specialty chemicals and women's apparel.

To further defend itself, ARC's board has authorized management to explore other alternatives, including recapitalization, leveraged buyout, sale of part of the assets of the company, internal restructuring or purchase of a "substantial business."

In addition, ARC said it is considering selling "a significant amount of stock to a third party" to "resist the Sequa offer," according to a filing with the Securities and Exchange Commission. Company officials have already had "preliminary discussions" with third parties, the filing said.

One security analyst who tracks the company said that, unless Sequa retreats, ARC may look for a "white knight" to remain independent. Either way, the analyst said, ARC is still "in play" as a takeover candidate and its ordeal is far from over.

The moves yesterday represented the latest chapter in a yearlong attempt by ARC to stay out of the clutches of hostile bidders. ARC's fight for independence had appeared to end successfully only last month when Clabir Corp. of Greenwich, Conn., abandoned its 10 month bid to gobble up ARC, selling its 12.3 percent of the firm to Sequa.

At the time, a jubilant Borten said he had been assured by Sequa officials that the company's purchase of ARC stock was "strictly an investment." But last week, after the Oct. 19 stock market crash had pounded ARC's stock, Sequa switched gears. Having already acquired 18.5 percent of ARC, Sequa made its $30 a share tender offer -- an offer that was conditioned on friendly acceptance from ARC. ARC's stock closed at $28.75 yesterday, down 25 cents.

In its court filing yesterday, ARC charged that Sequa "has misrepresented its intentions ... by stating that its acquisitions of the {ARC} shares were solely for investment at a time when Sequa's purpose had become to ... attempt to acquire the company by means of materially misleading and false disclosures and at substantially less than its fair value."

The suit, which asks for an injunction barring Sequa from any further purchases of ARC stock, accuses the company of violating the Securities Exchange Act and the Racketeer Influenced and Corrupt Organizations Act.

Under the golden parachute provision, if new management takes over, Borten would receive a lump sum payment equal to twice his annual salary and bonus, or about $576,000, according to executive compensation figures included in ARC's filings with the Securities and Exchange Commission yesterday.

Also entitled to lump sum payments are W. Gerald Hamm, executive vice president and chief operating officer, who would receive about $517,000, and Christopher W. Robertson, senior vice president, who would receive about $394,000.