Thrift industry leaders and regulators yesterday disagreed on long-term solutions for the ailing federal fund that insures deposits at savings and loans, but they threw united support behind out-of-the-ordinary bookkeeping techniques that keep hundreds of sick savings and loans alive.

Executives and federal accounting officials said at a House Banking subcommittee hearing that the Garn-St Germain Act of 1982 should be extended when it expires April 15.

Officials from the Federal Home Loan Bank Board, the General Accounting Office, the U.S. League of Savings Institutions and the National Council of Savings Institutions told Congress to renew the law.

The unanimity came despite acknowledgement by several of the officials that the unusual accounting methods allowed by the law have helped to mask the severity of the S&L industry's problems.

The act enables the Federal Savings and Loan Insurance Corp., which insures S&Ls, to boost the assets of ailing thrift institutions by issuing FSLIC notes. The notes push up an S&L's net worth -- the difference between assets and liabilities -- enough to permit the institution to meet federal requirements.

FSLIC needs to keep many sick thrifts going because merging or closing them would bankrupt it.

The act also allows holding companies, thrifts and a variety of other companies to cross state lines and buy ailing thrifts. Citicorp and Chase are among the banks that have used the purchase of ailing thrifts to circumvent laws preventing interstate banking.

Witnesses and congressmen agreed that the law is a necessary evil to buy time while a longer-term solution to the S&L crisis is sought.

Agreement on Garn-St Germain followed two hours of disagreement over the extent of S&L problems.

The U.S. League, a lobby group for S&Ls, testified that limited service "nonbank" banks undermine the health of S&Ls and should be banned. The National Council, another thrift lobby, said nonbank banks benefit the industry and should be allowed.