An attempt by President Bush to keep his savings and loan rescue plan from inflating the short-term federal deficit will add billions of dollars to the eventual cost, congressional leaders say.

Bush wants to pay for part of the rescue by selling $50 billion in "off-budget" bonds over the next three years through a special government-sponsored corporation. That way, the government could spend $50 billion that would not show up on the books as part of the budget deficit.Senate Banking Committee Chairman Donald W. Riegle Jr., D-Mich., said Wednesday that figures compiled by his staff show the off-budget mechanism will cost the government an additional $4.6 billion over 30 years.

Meanwhile, James Blum, acting director of the Congressional Budget Office, told the House Ways and Means Committee that the administration's plan would boost the government's interest payments by $100 million to $200 million a year.

But Treasury Secretary Nicholas F. Brady vigorously defended the arrangement Wednesday before Riegle's committee, which conducted the first congressional hearing on the 21/2-week-old plan.

Brady acknowledged that the bailout could be financed on-budget through regular, long-term Treasury borrowing but said that would be at a cost of "one less Trident submarine or no day care."

Brady also was sharply questioned about whether the administration is proposing a big enough rescue to put the industry on a sound footing. He said that not only would the plan provide money to close 350 insolvent institutions and meet the commitments on 205 failed S&Ls rescued last year, it would provide $24 billion from 1992 through 1999 to handle the possible failures of another 150 weak institutions.

The Treasury secretary was scheduled to testify to the House Banking Committee Thursday, while Federal Reserve Chairman Alan Greenspan was due before Riegle's panel.

Riegle told reporters after Wednesday's hearing that he was keeping an open mind, but so far could find no reason to favor an off-budget arrangement.

"If there are advantages, they're not obvious to me. . . . I think you start from the premise that you ought to keep the cost to a minimum, especially when you and your folks and your neighbors are going to have to pay for this problem, or a large part of it," he said.

Rep. Henry B. Gonzalez, D-Texas, chairman of the House Banking Committee, said in a 13-page analysis of the Bush plan that taxpayers would save $138 billion over 30 years if Congress directly appropriated the S&L money.

But, he conceded, that "would require a special tax earmarked solely for the purpose of financing the savings and loan bailout" and "administration policy and political reality may rule out this more direct approach."