Although President Reagan calls his economic program a four-pronged affair, it rests on a fifth ingredient essential for the plan's success. That element is the hope, or expectation, of the White House that Americans in fact will use their tax savings in a way that dampens inflation rather than stimulates it.
If the Reagan administration is wrong -- if Americans pour billions of dollars into buying consumer goods or gold, antiques, Persian carpets, and other hedges against inflation -- the battle may be largely lost.
In dollar terms, critics contend, nearly half the tax savings under Reagan's plan go to the top 10 percent of income earners.
This is precisely what the President's advisers intended. Because these top-drawer earners pay 45 percent or so of all income taxes, they are the ones most likely to put substantial tax gains into savings or investment.
The other 90 percent of taxpayers -- many of whom are driven to the wall by soaring food, fuel, and other prices -- are expected to spend the bulk of their more meager tax savings.
"To get the 10 percent that is economically necessary," said a leading conservative economist, "the President had to do what is politically necessary -- give the same percentage tax cuts to the 90 percent."
This is less hard-nosed than it sounds, because Reaganites are convinced that the tax package will benefit everyone down the road -- by spurring production, putting more people to work, and lowering inflation.
Some experts discount the risk of demand being pumped up by the tax cuts, especially if compensatory budget cuts are enacted by Congress.
"The structure of the Reagan tax cuts is not all that bad," says Rudolph G. Penner, resident scholar at the American Enterprise Institute. "First, you have faster depreciation on business investments, which have a supply-side effect."
"Second," Dr. Penner said, "there is a pressing need to cut marginal tax rates at the top, because inflation has pushed so many people into higher tax brackets."
He foresees a possible risk of a different sort, as the Reagan package works its way through Congress. "What happens," asks Penner, "if it starts being whittled away by special interests -- barge owners, or supporters of the Export-Import Bank? Will it then fall apart? I just don't know."
"If Reagan, or Congress, tests the wind too much [on what special interests are thinking]," says Sen. Jake Garn (R) of Utah, "then we will fail.
"Everyone," says Mr. Garn, chairman of the Senate Banking Committee, "is in favor of some part of that budget. Unless we make some people very angry, we are going to fail - just as Carter and Ford did."
A number of senators, in the wake of President Reagan's address to a joint session of Congress, spoke of their concern that the tax package would turn out to be inflationary and would swell the budget deficit.
"I have no doubt," said Garn, "that simple, individual tax cuts without expenditure cuts would increase the deficit. If we pass a tax cut without spending cuts, I would advise the President to veto it."
White House officials are pressing for at least a down payment on budget cuts before Congress reduces taxes.
All the economic goals of the Reagan program, says Murray Weidenbaum, chief White House economic adviser, are based on the assumption that the entire packa ge will be passed -- not just parts of it.