Martin Marietta Corp. announced yesterday an offer to buy 30 percent of California Portland Cement Co. in a transaction valued at about $62 million in cash.

In a separate corporate development, United Services Life Insurance of Washington reached an agreement to acquire Bankers Security Life Insurance Society. Both are affiliates of International Bank of Washington, a financial services and merchant banking company.

Bethesda-based Martin Marietta, whose cement subsidiary produced record sales of $181 million last year from plants east of the Rockies, said it offered to buy the entire common stock holdings in California Portland of the Dan Murphy Foundation.

Currently, the foundation owns 1.32 million shares, for which Martin Marietta will pay $47 a share in cash subject to necessary approvals. Martin said there have been no negotiations with California Portland, which operates plants in California and Arizona.

In the unrelated merger announcement, United Services said it would acquire Bankers through an exchange of 1.5 shares of United for each share of Bankers. If the transaction is completed, Bankers would be the surviving company but would be a wholly owned subsidiary of United.

The companies said United would benefit by acquiring a company that markets a general line of life insurance, to add diversity for United's business-the sale of insurance to military personnel and other government employes. Combined, the firms have $6.4 billion of life insurance in force.