The Federal Home Loan Bank Board has approved the merger of three out-of-state savings and loan associations into Home Savings & Loan Association, of Los Angeles, increasing the assets of the nation's largest S&L to almost $14 billion.

It is the 23rd federally assisted merger this year, further underscoring the severity of the financial crisis faced by savings institutions.

Home, which has been the nation's largest S&L for more than a quarter of a century, converted from a California stock charter to a federal stock charter as part of the transaction.

Under terms of the agreement, Security Federal Savings and Loan of Sikeston, Mo., Hamiltonian Federal Savings and Loan of Ladue, Mo. (St. Louis) and Southern Federal Savings and Loan of Broward County, Fla. (Pompano Beach), will operate as divisions of Home.

As part of the transaction, Home, which is the principal subsidiary of H. F. Ahmanson, of Los Angeles, has changed its name to Home Savings of America.

Ahmanson said that under the merger agreement, Home will acquire all the assets and liabilities of the three S&Ls. The company also said that arrangements had been made to ensure that none of the merged associations would show a negative net worth on its books at the time of the merger.

Bank Board officials would not disclose details of any financial assistance that might have been provided by its Federal Savings and Loan Insurance Corp. in negotiating the mergers. The agency also refused to release figures that would indicate the financial condition of the three S&Ls acquired by Home.

"This was an FSLIC-assisted merger and that speaks for itself," a Bank Board spokesman said in response to questions Friday.

The agency did say, however, that financial assistance required to facilitate the merger "shall consist of protection from losses related to real estate now owned by the acquired associations."

Further, Home will be protected from future losses on any real estate acquired through foreclosure of existing mortgage loans held by the three associations that it acquired, the agency explained.

The merger will increase Home's assets from $12.83 billion to $13.8 billion. Southern had assets of $612 million and operated 13 branches prior to the merger. Hamiltonian had assets of $236 million, and Security had $83 million. The two Missouri S&Ls operated nine and seven branches, respectively.

It is the fourth interstate acquisition to be approved by the Bank Board this year since the regulatory agency announced its policy in March of permitting such mergers negotiated by the FSLIC.

The present policy covering supervisory mergers is designed to reduce drains on the FSLIC fund by allowing interstate acquisitions to proceed when attempts fail to produce an intrastate marriage of S&Ls.

The first such merger was approved in September when West Side Savings of New York and Washington Savings of Miami Beach were merged into Citizens Savings and Loan of San Francisco, a subsidiary of National Steel.

That was followed by a merger of First Federal Savings and Loan Association of Broward County, Fla. (Fort Lauderdale), into Glendale Federal Savings and Loan Association, Glendale, Calif. Also, Boca Raton Federal Savings and Loan Association of Boca Raton, Fla., and Mohawk Savings of Newark were merged into City Federal Savings and Loan of Elizabeth, N.J.

In a related development announced late Friday, the Federal Deposit Insurance Corp. approved the expected intrastate merger of Union Dime Savings Bank, of New York, into Buffalo Savings Bank, of Buffalo, N.Y. As a result, Buffalo becomes the fourth largest savings bank in New York state and fifth largest in the nation.

Prior to the merger, Buffalo Savings had assets of about $3 billion and Union Dime had assets of about $1.4 billion.

The federally assisted merger "maintains public confidence in the banking system, and avoids the much higher cost of a deposit payoff," said FDIC Chairman William Isaacs.

The FDIC estimated a deposit payoff would have drained about $350 million from the federal bank insurance fund. In contrast, Friday's merger was expected to have a gross cost of about $166 million.