About 42 percent of the federally insured savings and loans in the nation are insolvent or have a dangerously low net worth, Rep. Stan Parris (R-Va.) said yesterday in a speech on the House floor warning of serious problems in the thrift industry.

Citing a recent General Accounting Office report that 434 members of the Federal Savings and Loan Insurance Corp. were insolvent as of last September, Parris said he has learned that another 25 thrifts have fallen into insolvency, bringing the total to 459. An insolvent S&L owes more money to its depositors and other creditors than it is owed by its borrowers and other debtors.

In addition, he said, another 909 institutions at the end of 1984 had a net worth of less than 3 percent, which is considered low. Net worth -- or what is left after liabilities are subtracted from assets -- is considered the most important factor in determining the health of a savings and loan.

"This independent analysis of the perilous financial condition of a significant portion of thrift institutions insured by the Federal Savings and Loan Insurance Corp. dramatically illustrates the problem faced by the fund," said Parris. "What's more, GAO's timely study exposes the strains a significant number of financially distressed thrifts have placed on the large majority of savings and loans who have labored to retain a margin of profitability."

A minority member of the House Banking Committee, Parris recently has become increasingly vocal about the health of the thrift industry. Parris said the GAO found that most of the federally insured thrifts in the worst condition are losing money. That finding, he said, rebuts industry claims that many of the ailing savings institutions will recover and, therefore, regulators don't have to be concerned about the low net worth.

The figures show "that the institutions with the greatest negative net worth are losing money at the fastest rate. That does not give you cause for great optimisim that they can work themselves out of these problems," said Parris.

The GAO reported that the large number of insolvencies means federal regulators could be hit with costs of $15 billion to $20 billion to rescue the 434 worst institutions. But the insurance fund has only $2.6 billion now available to deal with the problems, Parris warned.

The worst situations were found to be in California, Texas, Florida and Louisiana.

Parris said he requested the GAO study because he was alarmed by reports of the potentially dangerous demands on FSLIC, which insures deposits at savings institutions.

Federal regulators require a 3 percent net worth as protection against losses. But so many institutions have dropped below the 3 percent minimum in recent years, that FSLIC cannot enforce the limit because it does not have enough cash to take over the weak S&Ls.

Parris said the $15 billion estimate of the cost of liquidating just the 434 insolvent institutions is based on the fact that in 1984 the average cost to FSLIC of bailing out failed institutions was 14.7 percent of the thrifts' assets. But he said this year, the cost is running closer to 20 percent. In Texas, federal regulators estimate the losses at some thrifts could go as high as 70 percent of assets. Parris said a high-ranking bank board official has told Congress the cost of rescuing the worst S&Ls could be $30 billion and $50 billion.

One proposal to rebuild the insurance fund has been to require industry to pay 1 percent of its deposits into the FSLIC fund. This would provide an additional $8.5 billion. But the GAO found that the proposal would force an additional 159 thrifts into insolvency, and make the net worths of 247 other institutions dangerously low, Parris said.

Parris said the FSLIC should consider a number of options, including getting funds from the Federal Home Loan Bank System, raising money through the money markets, setting up a federally chartered savings and loan to help dispose of problem assets, and merging the FSLIC with the commercial banks insurance fund. He said, however, that there are problems with all these alternatives.