In the biggest settlement ever of a federal securities fraud case, administrators of the estate of the late Howard Hughes have agreed to pay at least $30 million to the shareholders of an airline acquired in 1970 by the billionaire recluse.

The settlement grows out of a case brought in 1975 by the Securities and Exchange Commission. It charged Hughes and others with conspiring to drive down the price of a then recently formed airline, Air West, in order to reduce the cost of acquiring it.

The settlement was presented yesterday in San Francisco to U.S. District Court Judge Alfonso J. Zirpoli, who has been hearing the case.

The $30 million is to be distributed to former stockeholders of Air West (since renamed Hughes Air West) who bought, held or sold securities in the airline between June 30, 1968, and April 1970.

The SEC alleged that in August 1968, the Hughes interests offered about $93 million for the assets of Air West. The airline had been formed in April of that year through a merger of three ailing West Coast carriers, Bonanza Airlines, West Coast Airlines and Pacific Airlines.

Hughes wanted to convert the publicly owned Air West into a private company under his wholly owned Hughes Tool Co. (now known as Summa Corp.). Holders of Air West common shares were promised $22 a share if they sold to Hughes Tool.

But when the acquisition was closed in April 1970, the Hughes interests decided that the assets of Air West were not worth $93 million after all. The value was set at only about $45 million, and the stockholders got only $10 per share from Hughes.

Several stockholder groups immediately filed suit against Hughes interests charging fraud and breach of contract. These suits were consolidated and were settled along with the SEC action.

The total settlement of the SEC and the private case will not exceed $37 million, according to an attorney involved in the litigation.

As a result of the settlement, an SEC attorney estimates that former Air West stockholders will get another $6 per share. It will be paid by Summa and Hughes Air West.

When he decided to go after Air West in 1968, Hughes hired James (Jimmy the Greek) Snyder to generate favorable publicity about the deal.

Snyder, now a professional odds maker and TV personality, was accused by the SEC of disseminating "false and misleading" information to the press and stockholders. He was enjoined from repeating those activities.

The suit says Snyder got "certain prominent political figures" to issue public statements criticizing the then management of Air West, which was resisting the takeover. Those same politicians, identified by an SEC source as Sen. Howard Cannon (D-Nev.) and former senator Alan Bible (D-Nev.), also praised Hughes. They received cash contributions from him, according to the SEC.

On May 11, 1976, while he was being interviewed by the SEC, Snyder took a swing at a government attorney.

Other defendants who settled with the SEC during the three-year litigation include Hollywood producer David B. Charnay, George Crockett, a retired industrialist, and former California congressman Patrick J. Hillings. All were accused of violating federal securities laws on behalf of Hughes. The three paid a total of $80,000 to Air West stockholders.

Three other defendants who were accused of manipulating the price of the stock of Air West to benefit Hughes are expected to challenge the SEC allegations in court. They are former Hughes aides Chester C. Davis and Robert A. Maheu, and Herman Greenspun, publisher of the Las Vegas Sun. If found guilty, these three face only a possible injunction against stock manipulation.

SEC Assistant Director Marvin Pickholz said that former Air West stockholders who want to claim under the settlement should write Douglas M. Schwab, 44 Montgomery St., San Francisco, Calif. 94105, or Jerome I. Braun 235 Montgomery St., San Francisco 94104. Both are attorneys for the stockholders in the class action suit.