Consumer, minority and women's groups last week began what they called a broadside attack on the insurance industry by filing antitrust class actions against the nation's 25 largest insurance companies.

The complaints were filed in California before the state commissioners of insurance, real estate and corporations and the secretary of business and transportation.

Lawyers announcing the action said the alleged practices under attack - including massive accumulation of real estate, interlocking directorates, employment discrimination, and a total lack of public accountability - are widespread throughout the country.

"We allege massive violations of the Clayton, Sherman and Cartwright antitrust acts," said Robert Gnaizda, an attorney with the San Francisco law firm of Public Advocates. (The Cartwright Act is California's antitrust law, which - unlike federal antitrust law - includes a prohibition on discrimination in employment.)

The insurance industry "operate in secrecy, and this secrecy is promoted by the insurance commissioner," Gnaizda said. "There is no public scrutiny of this industry."

The complaint was joined by the National Organization for Women, the western region of the NAACP, the League of United Latin American Citizens, San Francisco Consumer Action, and four other groups. Among its charges are that insurance companies:

In possible violation of antitrust law, are investing in both the savings and loan and real estate markets in California to such an extent that Prudential Insurance, the nation's largest insurance company, in 1975 had two and a half times as much in real estate mortgages ($12.3 billion) as Bank of America, the nations largest bank.

Are guilty of considerable job discriminiation against women and minorities, as indicated by a preliminary one-year investigation by the state Division of Fair Employment Practices. (The division has since focused its investigation on 300 insurance companies operating in Carlifornia; there legal challenges by insurance companies to the investigation are pending in southern California superior and federal courts.)

Discriminates against minorities and women by frequently refusing to sell them insurance when they seek to buy homes, thus adding to the practice called redlining - discrimination in lending against certain neighborhoods.

Allow their directors also to sit on the boards of banks, constituting a conflict of interest because insurance companies and banks are supposed to compete for consumer credit.

The complaint also charged that the state insurance commissioner, Wesley Kinder, "has not even compiled data on the industry, much less regulated it," making it difficult to obtain information on possible antitrust violations.

Kinder was out of town last week and is not available for comment, but an attorney in his office called the complaints "more of a sophisticated public relations thing," and said no staturory basis existed for such an action.

Spokesmen for several of the large insurance companies named in the action, including Prudential and Equitable, said they had not yet learned details of the complaint and could not comment on it.

The complainants want the secretary of business and transportation to prepare within 120 days an insurance industry "consumer-oriented corporate responsibility code." The code would require companies with more than 1,000 employes to include one-third public representation on their boards of directors, force in annual compilation of all insurance company real estate holdings (with analysis of thos holdings' effect on lending practices and inner city well-being), and oversee affirmative action plans for all insurance companies of more than 100 employes.