Up to 10 percent of the nation's savings and loans are in "severe trouble," and even tripling insurance premiums to boost the Federal Savings and Loan Insurance Corp. fund by $1 billion would be insufficient to cover expected failures, the top industry regulator told a congressional subcommitte yesterday.

Edwin J. Gray, chairman of both the Federal Home Loan Bank Board and the FSLIC, testified in executive session of the House subcommittee on commerce, consumer and monetary affairs that between 250 and 300 savings and loans were on the FHLBB's troubled list, sources said. Comparisons with previous years are impossible because the bank board has not revealed the number of S&Ls on its troubled list in recent years.

Unlike the bad days in 1981-82, when soaring interest rates left S&Ls with low yields on their mortgage portfolios, bad loans and investments are now the culprit, which regulators consider a greater threat to the insurance fund. For example, the number of mergers of S&Ls arranged by regulators because of interest rate problems was cut in half last year, whereas the number of liquidations caused by bad assets rose by 50 percent.

Some of the S&Ls now in severe trouble were involved in direct equity investments in condominiums and office buildings, sources said. Such investments are considered riskier than mortgages, although Gray declined to pinpoint this practice as the primary cause of their troubles. The collective assets of those S&Ls are said to be large and those institutions' failure would heavily impact on FSLIC.

Indeed, the assets of all S&Ls covered by FSLIC insurance increased by 17 percent last year while the FSLIC fund declined for the first time in history by over $400 million to less than $6 billion. The Federal Deposit Insurance Corp. fund, which covers bank deposits, and banks themselves in general are in much better shape.

The problem, Gray told the House Appropriations Committee last week, is that there are not enough financial institutions willing or able to take over savings institutions with bad assets. Candidates have become scarce because commercial banks and other financial institutions that have taken over thrifts in the past to expand geographically can now acquire or establish nonbank banks at less cost.

The executive session of the subcommittee was followed by the first of two open hearings on the condition of thrifts and banks. Subcommittee Chairman Doug Barnard Jr. (D-Ga.) declared, "Our nation's financial institutions have entered a deregulated environment with substantially increased opportunities, but with comparable risks as well. Accordingly, some fundamental reappraisals of the way financial institutions do business, the manner of their supervision, and the basis on which deposits are insured are urgently in order."

In addition to increased premiums, the bank board plans to impose higher net worth requirements on rapidly growing S&Ls and to limit direct investments over 10 percent of assets of shaky state-chartered S&Ls by requiring prior regulatory approval.

Gray did say that if Congress permits regulators to charge variable insurance premiums based on relative risk, they might lift the controversial direct investment regulations. He also supported the creation of state insurance funds to insure deposits at state-chartered thrifts that now are federally insured. Six states now have non-FSLIC insurance funds.

The issue for Congress is whether state-chartered, federally insured S&Ls should be allowed to incur greater risk than federally chartered S&Ls; federal standards for all raise the question of states rights.