Three major stockholders of Equitable General Corp. have launched an effort to oust President Charles Phillips and to restructure the board of the local insurance holding company.

In a "Dear Fellow Shareholders" letter mailed this week, the dissidents accuse Phillips and Equitable General's management of "gross mismanagement, poor business judgment, breach of fiduciary responsibility and conflict of interest."

And in a lawsuit filed in Fairfax County, the same shareholders demand that Phillips and six other board members pay back nearly $2.9 million that allegedly was misused in buying back shares of the company's stock.

The dissidents say they will propose setting 72 as the age limit for directors at equitable General's annual meeting on April 25. The limit would force out Phillips, who is 75.

"After 42 years at the helm and at nearly 76 years of age, it is time for Mr. Phillips to relinquish the reins of the company," say the dissidents.

Phillips yesterday said he is not about to step down, will vigorously fight the lawsuit and will answer the critics at the company's annual meeting, as they have asked.

Equitable General is a McLeanbased corporation that owns Equitable Life Insurance Co. and a small real estate subsidiary, First Elico Corp.

Attempting to launch a palace revolt are three shareholders who own some 300,000 shares, representing a $7.5 million investment at today's stock prices. They are:

Curtis Steuart, chairman of Steuart Investment Co., owner of 70,000 shares. He was forced off the board of Equitable Life in January by Phillips.

Marshall Garrett, son of the late Clyde Garrett, general counsel to Equitable for 25 years, who owns 203,000 shares.

Andrew Altmann, a former law partner of Clyde Garrett and also a former Equitable counsel, who owns or controls 29,000 shares.

Their attorney, Robert Smith, said yesterday the three considered a proxy fight against Equitable General's management but decided against it after studying the stockholder lists.

"They couldn't win," Smith said. Phillips owns 454,000 shares of the company - about 15 percent - and "could get 50 percent of the vote without even trying," Smith said.

Instead, Garrett, Steuart and Altmann took their case to the courts and the stockholders, raising identical issues in each forum.

Their complaints date to 1974, when Equitable Life, a District of the Columbia business, formed Equitable General as a Virginia corporation so it could expand into new businesses outside the insurance field.

Equitable General vowed to acquire new ventures, but after four years has bought nothing but 500,000 shares of its own stock. "We question whether any of these purchases has served a valid corporate purpose," says the dissidents' letter.

The latest purchase of stock, 315,000 shares bought in January of this year, is the subject of the lawsuit. The stock had been owned by Commercial Credit Corp. of Baltimre, which indicated last July it wanted to sell.

The dissidents say Phillips rejected the offer and the stock was sold for $26.25 a share to American General Insurance Corp., a Texas firm, which also got an option on another 37,000 shares owned by Control Data Corp.

When American General indicated it might try to take over Equitable General, the local company started fighting, buying off the bid in January by purchasing the stock for $32.50 a share when it was selling at about $26.

The critics contend Equitable General had nothing to gain from the stock purchase, and say the $1.89 million premium should be repaid to the company by Phillips and the directors.

Phillips defended the stock buy, yesterday, saying it was necessary to head off a hostile takeover that would have affected Equitable General adversely.

The lawsuit also accuses Phillips and the board of acting illegally to acquire the additional 37,000 shares from Control Data. The Company spent $988,000 for the stock, paying $26,25 when the shares were trading in the $23 range, the lawsuit complains.

That purchase was illegal because it never was approved by the board of directors, the lawsuit says. Phillips said the executive committee of the board approved the deal, but the dissipendent board member to maintain that in board minutes.

The letter to stockholders said the stock purchase is typical of the way the company has been run: "For many years, Mr. Phillips had conducted the business affairs of Equitable General as if it were his own private corporation with a more or less rubber-stamp board."

Five of the company's nine board members are outsiders, the critics acknowledge, but that means Phillips needs the support of only one independent board member to maintain control. The critics contend seven of the nine board members should be from outside, and demand an age limit of 72, forcing out Phillips.

The critics contend Phillips should be replaced by "a more agressive and enterprising Chief Executive Officer who will pursue the mandate of the reorganization to expand and diversify."