The Federal Home Loan Bank Board voted yesterday to require federally insured, state-chartered savings and loan associations to get prior government approval for direct investments in real estate, service corporations and equity securities when those investments amount to more than 10 percent of their assets.

The proposal, which is designed to reduce risky investments and thus the drain on the federal insurance fund by failed institutions, could affect some 1,450 savings and loans, particularly in California, Texas and Florida. It also comes a short time after the board proposed tightening net worth requirements to limit growth of savings associations that do not have sufficient capital. Large S&Ls would have to raise net worth by 5 percent for growth of 25 percent or more.

Comments on the board's decision on direct investments will be accepted for 30 days.

"The regulators are using a sledgehammer approach, just the way they did on brokered funds," said one industry executive, noting that abuses had not been proven. Another official, William B. O'Connell of the U.S. League of Savings Institutions, complained that the bank board should not be dealing with direct investment before seeing how net worth changes work.

The proposal highlights the conflict between deregulation and federal deposit insurance in which premiums are unrelated to risk. Federally chartered savings and loans are barred from equity investments; participation in service corporations is limited to 3 percent of assets.

However, states such as California and Texas permit state-chartered thrifts to put 100 percent of their assets in direct investments that include such things as windmill farms, horse breeding and stretch limousines. A recent survey by Robert Charles Lesser & Co./Ernst & Whinney revealed that 57 percent of S&Ls surveyed are now involved in real estate joint ventures and direct development.

Yesterday's version reflected some modification by the board of its previous position. Savings and loans would be able to exceed the 10 percent, or twice net worth, threshold on direct investment -- whichever is greater -- by getting permission from their principal supervisory agent at the Federal Home Loan Bank in their district. If no answer is received within 30 days, the investment could take place.

The agent would be directed to approve the investment if the S&L had good management, adequate capital and met the requirements for mortgage-related activities. Disputes would be arbitrated by the board. S&Ls could buy stocks listed on the New York and American exchanges, and the Nasdaq, but would require permission to buy local issues.

The National Council of Savings Institutions declared, "Despite the improvements, we remain deeply concerned about the unnecessary federal preemption of the authority of state governments to determine the extent to which the savings institutions they regulate may make direct investments."

FHLBB Chairman Edwin J. Gray said the idea was for regulators to get involved before the fact. He stressed it was not meant to curb investment. But industry observers still described it as a limit. One remarked it was tantamount to control by Washington and could be subject to political directives.