After a bitter three-year organizing effort, the Equitable Life Assurance Society and the union representing 54 female clerical workers in Syracuse, N.Y., yesterday announced a contract settlement that represents the first recent successful unionization of clericals at a major insurance company.

The three-year pact between the nation's third largest insurer and District 925 of the Service Employes International Union calls for an end to the 18-month AFL-CIO boycott against Equitable. The boycott was started because of the company's prolonged legal efforts to resist unionization.

While it affects a few workers, the settlement is "a tremendous step for unions," said Charles McDonald, AFL-CIO assistant director of organizing, because unionizing the mostly female and low-paid financial industry has been viewed as "almost impossible" by unions.

Fewer than 4 percent of workers in insurance and banking are unionized, and most are nonclerical workers.

In a statement yesterday at its New York headquarters, Equitable said, "We are pleased that the terms of the agreement fall within the framework of our long-term business plans."

The company said it also has pledged to keep the Syracuse office open at least through June 1987, a reference to earlier announcements that it would close its lone unionized facility.

Equitable said that "in return" for the settlement, the service employes' union agreed to have the boycott lifted and "to urge other unions to bring their pension and welfare business to the Equitable."

The company manages more than $50 billion in assets, much in pension funds, and the boycott by more than 90 AFL-CIO unions was considered a serious threat because of huge pension monies controlled by unions.

The contract calls for wage increases totaling 14 percent over three years and modifies what the union calls a "piecework" pay system based on the number of insurance claims processed and on supervisors' evaluations.

Employes had objected to having pay based partially on such "subjective" factors as "attitude," and the settlement eliminates that factor, company and union spokesmen said

Karen Nussbaum, president of SEIU District 925, said the contract also contains "terrific language on automation," which she said guarantees safeguards for operators of video display terminals, including additional rest breaks and provisions dealing with redesign of work stations.

"The working conditions were archaic, and these provisions deal with some serious problems" that helped prompt the union effort, she said.

A majority of the Syracuse employes, then numbering more than 90, petitioned the National Labor Relations Board in 1981 for union representation and voted in February 1982 in an NLRB-supervised election to unionize.

Equitable protested the election, while the union charged the company with refusing to bargain, as required by law. During two years of appeals, the NLRB upheld the union position, and the boycott was called to pressure the company to bargain.

The agreement also includes a provision in which Equitable agrees not to hire "labor-management consultants" to resist future organizing efforts.