The government's Export-Import Bank is $4 billion to $6 billion in the red and the figure could reach $10 billion by 1992, the chairman of the House Banking Committee says.

"With the billions it will cost to fix the Federal Savings and Loan Insurance Corp. fresh on our minds we must surely face the Eximbank's insolvency, which was heedlessly disregarded by the Reagan administration," the chairman, Henry B. Gonzalez, D-Texas, said Wednesday.Gonzalez was referring to the savings and loan crisis. The Eximbank lends mostly to Third World countries to encourage sales of American goods.

"The Export-Import clearly fulfills a very useful, even essential purpose," Gonzalez said. "It creates jobs domestically and helps our export industry lower our massive trade deficit.

"But the Eximbank is insolvent. This means the budget deficit and cost of subsidizing our export industry are both understated by $4 to $6 billion.

"We have seen with the tragic FSLIC crisis that masking the true insolvency of a government agency has disastrous results and the taxpayer ultimately bears the burden of this irresponsibility."

William Ryan, the bank's acting president, replied that normal accounting practices do not apply because the bank is backed by the full faith and credit of the federal government.

Gonzalez complained that it still carries as assets loans made to Cuba before President Fidel Castro took over and to China before the victory of the Communists on the mainland.

"Eximbank has not received a cent on these loans in over 40 years," he said.

Ryan said these were debts of sovereign countries and there is some hope of collecting them.