The blunt-instrument assault on Ronald Reagan that so outraged editorial commentators has planted fears of war in the minds of American voters that will result in President Carter's reelection unless Reagan's coasting campaign stirs itself into dramatic response.

The abrupt turn of events was first reflected in a variety of polls beginning Oct.7 and accelerated over the weekend of Oct. 11. President Carter's remorseless campaign was working. He had passed Reagan in Ohio, Illinois and possibly Texas, taken a big lead in New York and pulled nearly even in Michigan, Pennsylvania and Florida. The momentum was all with the president three weeks before Election Day.

The non-response by the Reagan campaign is a clue to how his big lead was dissipated. At a moment of crisis for his candidacy, the Republican nominee and his entourage were off on one of their periodic transcontinential migrations to California. Reagan himself rested, while his staff leisurely conferred. There was no emergency meeting, because there was no sense of emergency.

By the beginning of the new week, reality was intruding on the Reagan campaign. But it remains to be seen whether the jerry-built high command can bring itself together for some decisive counterstroke; a revitalized media campaign, a special half-hour televised speech, even a debate challenge.

Actually, polling across the country still shows overwhelmingly negative reactions to both Carter and Reagan (and, lately, Rep. John Anderson as well). The difference is that the public thinks that Carter merely ruined the economy while Reagan might start World War III. "I can guarantee that the American public will absolutely not vote for anybody it thinks will start a war," one worried Republican strategist (not on the Reagan high command) told us.

This is testimony to the effectiveness of Carter's strategy. Looking at pollster Patrick Caddell's survey's last summer, campaign manager Hamilton Jordan knew from the start that the president's only hope was to paint Reagan as a man of war. "Just wait till we get to the housewives," one Carter strategist gleefully predicted. With Jordan as Mr. Inside and Robert Strauss as Mr. Outside, this has been the whole of the Carter campaign.

Whenever behind in past political campaigns, Carter's response has been to assault his opponent. It has worked before, and it is working this time. The president himself did overplay his personal attack and apologized so that, as one Carter insider said privately, he "could continue to do what he was doing before." More important, media expert Gerald Rafshoon's crispy directed TV spots each night proclaimed the connection of Reagan and war.

This has received incomparable aid from the familiar Republican propensity to sit on a lead, though this time there was no proper lead; Reagan never surpassed 40 or 41 percent, not enough to win unless Anderson's vote held firm. The primary Reagan tactic was caution: avoid mistakes.

That was embodied in the TV spots prepared for Reagan by Los Angeles advertising executive Peter Dailey. The so-called "California documentary," showing Reagan saving his state from backruptcy in 1967, has become a staple of prime-time television -- unrelated to Carter's attacks or, indeed, to the political world of 1980.

Complaints about Dailey's sleepy spots by Republicans who previewed them have resulted in unanswered phone calls and no action. There has been no coordinated media response to the Carter onslaught. "We are coasting," conceded one Reagan insider, unaware that new polling data show them coasting to defeat.

Starting Oct. 7, pollsters around the country began to catch the Carter trend, but the Reagan campaign was oblivious. On Oct. 10, Reagan strategists in Washington brainstormed how to counteract the "October surprise" that they feared the president would conjure up to overtake Reagan. Other Reagan insiders grappled with the "Reagan administration's" transition. One senior Reagan aide confided that the election was won.

Assuming that reality has penetrated this euphoria, no quick response is at hand. It is late in the day for new TV advertising. Some Reagan advisers believe the answer might be to buy a half-hour of prime time for Reagan to go into the American voter's living room to talk about national security, foreign policy and -- mostly -- peace.

Or, a more dramatic response: accept Carter's debate challenge, renewed over the last weekend by Strauss. "I think the governor [Reagan] always wanted to debate," one aide told us. But none of his senior advisers did, particularly those former associates of Gerald R. Ford whose first choice for president when the year began certainly was not Ronald Reagan. Their lack of confidence in the candidate led to Reagan's coasting, which could well be a slow route to oblivion.