American Health Services Inc., a Washington manager of hospitals and health care facilities, is studying a plan to "go private" by merging AHS with a new firm-which would be formed by principal stockholders as a privately held business.

According to an announcement, the plan was given to the AHS board of directors recently by the principal owners-three private corporations that own 62 percent of common stock.

Under terms of the proposal, other common stockholders would receive unsecured debentures in exchange for their holdings.An unidentified investment banking firm has been hired to evaluate fairness of the consideration to be paid to minority common share-holders in the proposed arrangement-a key factor in any plan to reverse public ownership, in terms of Securities and Exchange Commmission surveillance of such deals.

AHS said its board approved the proposal in principle, subject to the judgment on debenture value of minority shares. The company has proposed unsecured, 10-year debentures with a face amount greater than the current quoted market value of common stock ( $6 bid, $8 asked in the over-the-counter market at the end of last week).

Melvyn Estrin, president; Dr. Hyman Frankel, vice president; Charles Abod, vice president and treasurer; and Dr. Sheldon Steinberg, a director, own 90 percent of the stock in the three private firms with a controlling interest in AHS.

Two-thirds of the firm's stock must be voted in favor of the proposal and the three principal stockholding corporations said they intend to vote in favor only if a majority of shares owned by the general investing public are not voted against the merger.

A meeting for the stockholders' vote is planned for June.

The hospital firm was incorporated in Virginia early in 1969. That same year, AHS sold 250,000 shares to the public at $10.25 apiece but the stock price plummeted in the 1970s, reaching less than $1 a share in 1975 before rebounding somewhat. The company has about 750 stockholders and 1,500 employes at 15 subsidiaries that operate psychiatric and general hospitals and health care centers in Virginia, Louisiana and North Carolina.

AHS has been consistently profitable, earning $1.50 a share in the year ended Sept. 30 compared with $1 in the previous 12 months as revenues rose to $21.3 million from $20.1 million.