'Prudent' Mondale

Exactly four years ago, then GOP presidential challenger Ronald Reagan laid out his economic plan for his four years in office. In a speech to the International Business Council in Chicago, he gave the much-sought details of how a Reagan economy would differ from Jimmy Carter's course to 1985. According to this newspaper's account: ''Reagan promised to balance the federal budget in two years, cut personal income taxes 10 percent for three years running, and still produce a budget surplus of $93 billion by fiscal 1985.

''Also, he would stunt the growth of federal spending. His economists project a Republican budget of $734 billion for the United States in fiscal 1985 - $212 billion less than the Carter administration's projected $946 billion....

''In political terms Reagan sought to counter Carter charges that the Republican list of campaign policies would, when added up, lead the nation to financial ruin. And he wanted to answer John Anderson's taunt that the GOP tax-cut scheme to create a budget surplus was a matter for 'mirrors.' ''

The Reagan promise and performance are instructive when examining Walter Mondale's economic blueprint, disclosed yesterday in Philadelphia.

Mr. Reagan did cut income taxes, after much give-and-take with Congress. And the spending mix changed. But he did not balance the federal budget in two years. The promised $93 billion surplus never materialized - indeed, the actual deficit is nearer twice that amount. And instead of spending $734 billion in fiscal 1985, the White House's own federal spending projection for fiscal 1985, rounding out four years of Reagan rule, is $925.5 billion, or $940.3 billion including off-budget outlays - extraordinarily close to Carter's projection.

One thing about Carter's last numbers: They were basically ''current spending'' projections; that is, they closely tracked the basic inertia of government spending patterns. That was one reason Reagan's first-year attempt to cut Carter's projected fiscal 1982 spending to $695 billion failed, ending up closer to Carter's original $736 billion. Further, Republican economists pointed out immediately in September of 1980 that Reagan's fiscal, monetary, and defense spending plans were on a collision course, with recession and deficits likely.

Whatever the fine print, the public got the rough idea that Ronald Reagan thought tax cuts would lead to a more energetic economy, one that could cover big defense outlays and still deliver a surplus. He used the neutral economic data from Congress as part of a strategy to reassure voters that his optimism was well founded.

Now four years later almost to the day, we have challenger Walter Mondale going through a similar political-economic routine. For Mr. Reagan's optimism Mr. Mondale is offering prudence. He promises a ''pay-as-you-go'' approach that would reduce a fiscal 1989 deficit of $263 billion (the Congressional Budget Office projection) by $177 billion, leaving an $86 billion deficit in that year. Mondale would modify Reagan's tax indexing program, limit the third year of the tax cut now in effect, add a 10 percent surcharge for married couples with incomes over $100,000 and single people earning over $70,000, impose a minimum 15 percent tax on corporations, limit tax shelters, and so forth. And to show voters that the ''tax and spend'' allegations of the Republicans are unfounded, Mondale would put the new revenue into a trust fund earmarked for paying off the deficit.

Another political signal runs through these figures: They would target middle-class and upper-income households and businesses. Families with incomes under $25,000 would have no tax increase; those earning from $25,000 a year to $ 35,000 would pay $95 a year more; those earning $35,000 to the low-$40,000 range would pay $205 a year more. Families earning more than $100,000 would pay $2,600 more.

Surveys show that most Americans are anticipating a tax increase under either Mondale or Reagan next year, whatever the two are saying now. Whether Mondale's votes is arguable. But, like Reagan's performance four years ago, it is descriptive of where his administration would stand.

We will know more in coming days and weeks, as the public weighs his economic pitch, whether voters feel this is a time for Mondale prudence vs. Reagan optimism.