Only six days before the election, Ronald Reagan finally fired at the fat Jimmy Carter targets of economics and incompetency -- a delay explaining how a potential Republican landslide became a cliffhanger subject to change by Iran's release of the hostages.

Reagan's belated start on what he should have been doing for months, coupled with favorable response to his debate performance, buoyed his final days of campaigning through tightly contested states. The beginning of despair two weeks earlier turned to guarded optimism. Reagan's private polls showed him seven percentage points ahead nationally -- enough to counter an estimated 1.5 to 2 percent surge by Carter because of a hostage release.

But why so late in doing the obvious? That question evoked anger and regret among senior advisers in the forward cabin of Reagan's chartered jet. They blame anemic Reagan campaign strategy that relied on public opinion surveys. "The damn polltakers took over," one adviser complained. Those polltakers put stress on building Reagan's positive image.

So it was the economics did not become Reagan's overriding theme until mid-October. Not until the day before the debate were weeks-old television commercials attacking President Carter's credibility finally put on the air. Not until Thursday morning, Oct. 30, in a New Orleans airport hangar, did Reagan systematically assault Carter's competency.

Recalling Carter's 1976 campaign promise of a government is good as the American people, Reagan told the New Orleans rally: "He only gave us a government as good as Jimmy Carter, and that isn't good enough."

That and other applause-getting lines were brand new. Ken Khachigian, a 36-year-old California public relations man who once wrote speeches for Richard Nixon, months ago applied for a job with the Reagan campaign, which turned him down as too expensive. Three weeks ago, with Reagan's rhetoric and poll ratings sagging, it was decided no price was too high. Thus, Khachigian's prose became Reagan's rhetoric in New Orleans and across the country.

Reagan's revived oratory coincided with post-debate good news. When Reagan arrived in New Orleans, senior adviser Stu Spencer immediately conferred with regional coordinator Kenny Klinge, who had new voter trackings: Reagan forging ahead in traditionally Democratic Louisiana and Missouri and no worse than even in overwhelmingly Democratic Arkansas.

In Pittsburgh that day, Reagan labor operative Michael Blazano, who had experienced trouble finding union officials for a Friday breakfast with Reagan, suddenly discovered plenty. The astute Gov. James Rhodes of Ohio told friends that Reagan had clinched the election when he closed the debate by asking Americans whether they were better off or worse off economically after four years of Carter.

Yet, that highly effective closing inexplicably was missing from Reagan's new economic/incompetency speech. He also omitted, in describing his 30 percent tax cut, any talk about incentive to invest, to save and to work; Reagan's defense was the tax cut as a Keynesian countercyclical recession-fighter.

Despite these imperfections, Reagan at long last was saying most of the right things. He ignored Carter's wild 11th-hour swings at him. Most important, the Republican presidential candidate was concentrating on bread-and-butter issues without the masochistic Republican call for sacrifice and austerity, ending his speeches with a vision of America based on growth instead of scarcity.

That this came so late is blamed by Reagan's bitter senior aides on the two California technicians who have dominated strategy: pollster Richard Wirthlin and advertising executive Peter Dailey. Against the instincts of Reagan's political aides, they insisted on avoiding harsh criticism of Carter and even Carter's record for fear of alienating undecided voters.

Since their polling data showed national unawareness of Reagan's post-Hollywood career, Wirthlin and Dailey insisted on running for two full months a lugubrious commercial on Reagan as governor of California. William Casey, Reagan's powerless campaign chairman, tried in vain to change the campaign's course. Not until the campaign's last week did Casey and the advisers aboard the plane -- James Baker, Lyn Nofziger and Stuart Spencer -- get the attack on Carter's competency launched.

Once begun, Reagan stuck to it diligently -- even in an overly long speech to uncomprehending high school students at Des Plaines in Chicago's critically important suburbs. He assailed "a record of almost complete economic failure" as the enthusiastic teen-agers booed the prime interest rates and budget deficits.

Had this started eight weeks earlier, would 8 percent unemployment, 12 percent inflation and a 14 percent prime interest rate have produced a GOP landslide? Pondering that question does produce bitter regret on the Reagan plane that they built no lead to guarantee withstanding the vagaries of hostage politics.