Seven Connecticut banks have joined together in an unusual move to take over a troubled savings institution there and prevent an out-of-state bank from gaining entry.

Permanent Savings of Meriden, the largest state-chartered thrift, will be liquidated and divided up among the seven. Permanent's branches will become branches of the acquiring institutions, which also will assume its assets and liabilities. An application for the arrangement was filed last week with the Federal Deposit Insurance Corp., which must approve the deal.

Regulators say that whereas a number of banks have acquired and swallowed savings institutions, this is the first instance of a thrift being dismembered in such a fashion. The case also illustrates the continued precariousness of the thrift industry and the intense competition in regional banking.

In 1981, Permanent, then prosperous, took over two failing S&Ls in a voluntary merger. However, Permanent failed to overcome the primary problem eroding thrifts at that time: paying more for its money than it was receiving on its loans. By last September, its net worth stood at $4.6 million, or 1.34 percent of assets. In January, its net worth had dwindled to less than $2 million on assets of $320 million.

With monthly losses of $300,000 to $450,000, Permanent could not survive long. The losses were attributed to an unfavorable interest-rate spread rather than bad loans or brokered funds, according to a banking official.

Last fall, state banking commissioner Brian J. Woolf determined that no institution in Connecticut was large enough to absorb Permanent. He feared that if a voluntary merger were not arranged, the Federal Savings and Loan Insurance Corp., which insured Permanent, would step in and organize a merger with an out-of-state institution. The FSLIC has permitted a failing California thrift, for example, to be taken over by a New York bank holding company.

Woolf said he was particularly concerned about the possibility of a New York bank being allowed in. The New England states have carefully crafted a pact to encourage interstate acquisitions among themselves but exclude the money center banks. Citicorp, one of those excluded, has fought back with a lawsuit questioning the constitutionality of the pact. The Supreme Court will review the issue this term.

Woolf solicited bids from Connecticut banks, which agreed to pay a premium for the right to assume Permanent's assets and liabilities. Permanent's main office and branch in Meriden will be transformed into an office of Connecticut National Bank. The other participants are City Trust, of Bridgeport; Colonial Bancorp, of Waterbury; CBT Corp., of Hartford; Connecticut Savings Bank, of New Haven; New Haven Savings Bank; and Society for Savings, of Hartford.