Ronald Reagan's clear reaffirmation Tuesday night of Kemp-Roth tax reduction as the heart of his economic growth program came only after yet another effort by his staff to retreat under Democratic fire.

Reagan reflexively objected to a draft of the economic speech that would have stretched the three-year 30 percent tax cut to five years. Like much else foisted on him of late by his advisers, that stretch-out was politically mindless. It would have properly exposed him to charges that he was conceding the anti-tax positions of his critics.

The avalanche of economic advisers from the Ford administration had suffocated tax-cut talk until Tuesday night's address in Chicago before the International Business Council. Most of Reagan's recent stump speeches have not even mentioned tax reduction. His new television spots soft-pedal the issue.

That is another example of the Reagan campaign deteriorating into a struggle between candidate and staff. While adies whisper comments to newsmen about the blundering candidate, the fact is that many of the campaign bloopers since the national conventions are more attributable to his staff than to Reagan.

This was pointed up Sept. 3 when Reagan and five outside economic advisers, he in a sport shirt and they coatless but wearing ties, met in the garden at Wexford, his rented Virginia estate. The draft -- prepared by Dr. Martin Anderson, a senior domestic policy adviser, and veteran Republican speechwriter William Gavin -- would have stretched Reagan-Kemp-Roth tax cuts over five years.

That set off alarm bells for the candidate. This must be changed back to three years, Reagan said. Rep. Jack Kemp, discussing issues face-to-face with Reagan for the first time in six months, naturally agreed. Less naturally, he was backed by Dr. Charls Walker, former deputy Treasury secretary who once pressed for a stretch-out but has now joined forces with Kemp.

For political justification, Reagan passed around a new Gallup poll commissioned by the U.S. Chamber of Commerce, which shows a 54 percent to 30 percent nationwide margin in support of a 10 percent rate reduction in taxes this year -- as proposed in the first year of Kemp-Roth. The same poll shows that only 24 percent of the voters think inflation would be increased by a 10 percent tax cut.

These figures should come as a surprise only to those politicians and journalists who seem to think that hard-pressed taxpayers really do not want relief. When we ask voters in our own door-to-door interviewing whether they favor an immediate tax cut, the response is usually positive -- and frequently incredulous that anybody would have to ask.

But the Carter theme that tax reduction is inflationary poison being forced on desperately resisting taxpayers had been making headway within the Reagan camp. Indeed, on the day of the economic meeting at Wexford, an astute Democratic strategist told us the Carter team's attacks had succeeded in stifling Reagan's tax reduction talk.

Besides insisting on the three-year tax reduction span, Reagan also was displeased with the vagueness of the first draft. To make his point, he told his advisers he would rather deliver an accompanying fact sheet than the speech; as a result, figures from the fact sheet detailing massive tax increases under the present system were inserted in his speech.

This is not merely sloppy staff work that is commonplace in the Reagan campaign. One Reagan-for-president leaflet, listing only Ford administration officials as the candidate's economic team, calls for tax reduction providing people "with more money to spend, creating a demand for more goods and services."

Such an argument is pure Keynesian, demand-side economics. It ignores supply-side economic theory behind the tax cuts, as stated by Reagan in Chicago Tuesday night: "More than any single thing, high rates of taxation destroy incentive to earn, to save, to invest. They cripple productivity, lead to deficity financing and inflation and create unemployment."

Here is a doctrine that Ronald Reagan believes strikes a most responsive chord with ordinary Americans in these days of economic stress, even if his staffers and the economists inherited from President Ford do not. But it had been so long since Reagan talked that way that many close listeners, including pleased Democratic politicians, thought he had forgotten his own lessons. In this as in much else, the candidate's sins can be traced to his staff.