WASHINGTON (AP) _ A key senator today attacked President Clinton's rescue package for Mexico as a ``billionaires' bailout'' that would not help the average Mexican, while a conservative economist charged that Republicans were wrong to support the Clinton plan.

Clinton, turning up pressure for the package in a speech to corporate and government leaders in Switzerland, warned today that ``failure to act could have grave consequences for the Mexicans, for Latin America, for the entire developing world.''

While support for Mexico has run into trouble on Capitol Hill, the country secured much-needed support from the International Monetary Fund. IMF officials, subject to approval next week by the agency's executive board, agreed to lend Mexico $7.8 billion over 18 months.

Treasury Secretary Robert Rubin said the IMF announcement underscored the desire of the international financial community to stabilize the situation in Mexico. Combined with the administration's proposed $40 billion loan guarantee, it should restore investor confidence in Mexico, he said.

``This package is the largest single package that has ever been put forth by the IMF,'' Rubin told the Senate Foreign Relations Committee.

Clinton's proposal encountered a second day of skeptical questioning from congressional committees.

Sen. Ernest Hollings, D-S.C., sought to dispute contentions by the administration that the loan guarantees are only a safety-net that will never be used because Mexico will be able to repay the loans that the guarantees are backing up.

``Of course, they are not going to repay,'' Hollings told the Senate Foreign Affairs Committee. ``Let's cut out on this nonsense of trying to hoodwink the American people. They are in desperate circumstances in Mexico.''

Hollings, an ardent foe of the North American Free Trade Agreement with Mexico passed in 1993 and the General Agreement on Tariffs and Trade passed last month, was the leadoff witness before the Foreign Affairs Committee, whose chairman, Sen. Jesse Helms, has also been a vocal critic of the administration's efforts.

``This is a billionaires' bailout,'' Hollings said, saying that it was designed to help Mexico's 44 billionaires and other rich investors and not the average Mexican worker.

Another witness, Lawrence Kudlow, former chief economist at the Office of Budget and Management during the Reagan administration, said that if Republicans support the Clinton plan ``the GOP will have betrayed its own core economic principles and turned a deaf ear to the electoral message of last Nov. 8.''

``Why would the United States force on to Mexico a set of discredited economic policies such as inflationary currency devaluation, large tax increases and wage and price controls that we ourselves would never think of using at home,'' Kudlow asked.

Clinton, in a speech today to the World Economic Forum, said he was confident the guarantee program would win congressional approval ``and will make a difference in the world economy.''

``It's the kind of response to address a problem before it spreads that the new world economy demands,'' Clinton said.

He said the rescue package is important to protect American jobs as well as the Mexican ecnomy, saying, ``it's the right thing to do for the rest of the world but it's also the right thing to do for America.''

William Seidman, former chairman of the Federal Deposit Insurance Corp., told the committee that the Mexican bailout bore disturbing similarities to the ``savings and loan crisis of the '80s and the banks considered too big to fail.''

``Huge market losses by mutual fund investors, U.S. banks and others in the foreign securities market are about to be eased by good old Uncle Sam. No wonder financial markets cheer,'' Seidman said.

Rubin, Federal Reserve Chairman Alan Greenspan and Secretary of State Warren Christopher testified before Helms' committee to defend the program.

The administration put forward the idea of $40 billion in loan guarantees for Mexico two weeks ago, hoping for quick congressional approval as a way of calming financial markets and halting a disastrous slide in the Mexican peso, which has lost almost 40 percent of its value against the dollar since Dec. 20.

The administration has argued that stabilizing the Mexican economy is in America's best interests, to keep illegal immigration from skyrocketing and because Mexico is America's third-largest export market.

``The stakes are high in avoiding a potential financial crisis that could spread to other emerging markets,'' Rubin told the House Banking Committee on Wednesday.

Greenspan warned that the situation was serious because of the threat it posed of triggering a flight of capital from other countries, not only in Latin America but also in Eastern Europe and Asia.

But opponents charged that Greenspan and the administration were attempting to create a false sense of panic in an effort to rush through Congress a huge bailout bill for investors.

House Speaker Newt Gingrich, R-Ga., and Senate Leader Bob Dole, R-Kan., said Wednesday that changes may have to be made to meet widespread objections. They said the administration will have to do much more to round up Democratic support.

``It's clear from polling data that there's just no base of popular support out there,'' Gingrich told reporters at a news conference.

While saying the measure could be salvaged, Gingrich said, ``No one should underestimate how much work is going to have to go into the next week or two.''