House Banking Committee Chairman Henry B. Gonzalez (D-Tex.) charged yesterday that the Treasury has been circumventing Congress in carrying out its international economic policies, running up a tab of billions of dollars that taxpayers will eventually have to pay.

"If we don't stop this unaccountable drain, we're facing a calamitous situation," Gonzalez said in an interview.

Although Treasury Secretary Nicholas F. Brady has sharply rejected previous criticism, Gonzalez said that in one of two specific areas under review -- foreign exchange market intervention -- the Federal Reserve Board concedes that further study is warranted.

The first challenge mounted by Gonzalez, however, relates to Brady's debt relief plan for Mexico, which involved a sale of U.S. zero-coupon bonds at what Gonzalez said was a price favorable to Mexico. The charge that Brady provided a back-door subsidy for Mexico has been denied by Treasury officials, and Undersecretary David C. Mulford, who was in charge of the deal, contends there were few pricing precedents.

But Gonzalez quoted General Accounting Office estimates "that the Treasury spent between $100 {million} and $300 million dollars of taxpayer money, without congressional approval, to help the commercial banks and Mexico complete their recent debt relief package."

Gonzalez acknowledged that there is as yet no GAO report on the zero-coupon bond sales but said that he quoted the figures from notes taken by a staff aide during an oral briefing May 24 by GAO officials on preliminary investigations.

GAO officials refused comment on Gonzalez's statement. But other sources indicated that the GAO had not yet made a final determination that the Treasury had chosen the wrong interest rate for pricing the bonds, or that the Treasury had forgone revenue it should have claimed. The Treasury, sources say, has great latitude in making such decisions, and there appears to be no legal issue.

Gonzalez, however, said he is raising a public policy issue.

"What is disturbing," he said, "is that this is one more channel through which the departments can operate without proper authorization or appropriation, just like the Home Loan Bank Board did when it committed the Treasury to spend $44 billion for the S&Ls without going through the appropriations process.

"The reason the Treasury wanted to make this deal for Mexico was that the State Department was under pressure with respect to debt relief for Mexico, so they favorably priced the zero-coupon bonds. This practice is dangerous and totally unacceptable."

The secondary controversy, relating to exchange rates, recently surfaced when three members of the policy-making Federal Open Market Committee of the Federal Reserve objected to loans by the Fed to the Treasury's Exchange Stabilization Fund for intervention purposes. They questioned whether the loans "could be viewed as avoiding the congressional appropriations process."

Gonzalez said he was outraged by a Mulford letter April 23 to the GAO in which he said that the Treasury secretary's decision on spending those funds is "final and may not be reviewed by another officer or employee of the government."

The congressman noted that the government, because of huge recent exchange rate interventions, is holding about 20 billion Japanese yen and nearly the equivalent in German marks that he said had shrunk in value by about $2 billion in the last six months. He said that foreign currency holdings, now more than $46 billion, amount to 65 percent of American reserve assets, compared with only 30 percent five years ago.