State savings and loan supervisors yesterday accused federal regulators of trying to destroy the dual banking system by denying federal insurance to new state-chartered savings associations in three states, and said they were considering legal action against the federal regulators.

William S. Bergman, executive vice president of the National Association of State Savings and Loan Supervisors, reacted to the revelation that the Federal Home Loan Bank Board has suspended approval of federal insurance for new state-chartered thrifts in California, Texas and Florida on the grounds of inadequate supervision. He called the board's new policy "unprecedented, unnecessary and perhaps illegal."

As a result of the moratorium, scores of new state-chartered institutions in the three states are in limbo, with millions of dollars committed, but unable to open without insurance.

The new government policy comes on the heels of a vote by the House banking committee last week to give federal regulators more power over state-chartered S&Ls. At the request of the bank board, the committee approved an amendment to a bill that would, in effect, give the bank board a veto over the type of investments state-chartered, federally insured thrifts can make. If the bank board disapproved of an investment, a thrift would have three years in which to divest itself of the investment.

Both actions by the bank board are aimed at curbing what Chairman Edwin J. Gray perceives as risky investments threatening the solvency of the Federal Savings and Loan Insurance Corp. fund. These activities include such non-housing-related investments as fast-food franchises and horse-breeding farms. If these investments fail, FSLIC, which insures deposits up to $100,000 per person, must pay the bill.

Federally chartered S&Ls can invest no more than 3 percent of their assets in non-housing activities through service corporations. However, California permits the S&Ls it charters to invest up to 100 percent. (A bill to cut that to 20 percent is now pending in the state legislature.) Florida allows 20 percent, and Texas permits 10 percent of an S&L's assets in such investments.

Bergman called Gray's moves "a one-two punch, an all-out assault against the state system." He said association attorneys are now studying whether the bank board can legally dictate the quality of state examination staffs when it has no standards for its own examination staff.

Florida was asked to sign an agreement whereby the state would provide an equal number of state examiners to join with federal examiners in audits of state-chartered institutions. The state's comptroller, Gerald Lewis, demurred, saying that such an "agreement merely reiterates what we have been doing for years. . . . We have adequate staff, 153 people. We have always conducted joint examinations on state-chartered thrifts. . . . We are shocked they they the federal regulators would threaten such extreme action as withholding insurance from new thrifts without explanation."

L. L. Bowman, commissioner of the Texas Savings and Loan Department, said he has 35 examiners and is planning to add five more to examine 220 state-chartered S&Ls. He said he would sign an agreement with the bank board provided "it does not box Texas into an untenable position. . . . I will maintain staff at a competent level. But the solution to the problem is not throwing untrained people in, but in better supervision."

The bank board has 750 examiners in the field and plans to add 130 more by year's end. In addition, the supervisory staff will be increased by more than 100. An examiner goes over an S&L's books on a regular basis; a supervisor works with an S&L to make sure it complies with the rules.