A week before, President Reagan had a commanding and unbeatable lead over his opponent; last week he was doddering, reeling, hoping for a rescue by his vice president -- in Washington.

In South Euclid, you get a different impression. There, on streets strewn with fall leaves and lined with white and blue Cape Cods and bungalows, you run into elderly women who don't vote any more, young mothers too busy with night school to register, and some people who come right out and say they're not going to tell you anything.

There are plenty of Halloween stickers on doors and windows already, but no lawn signs or bumper stickers. Most of those with definite opinions seem to have had them confirmed by Sunday's debate. There is the 40ish grandmother who is strongly for Mondale and says of the president, "I don't think he does well by himself." And the bearded man who approves of lower inflation, disapproves of the military buildup, and favors firmly "the lesser of two evils" -- Reagan.

"The reason I know Mondale is in trouble," says Matt Hatchadorian, the Republican candidate for Congress in the 19th district of Ohio, "is that in Parma and Euclid" -- working-class Democratic towns -- "the issues I hear about from voters are, first, jobs and economic growth and, second, taxes." Hatchadorian has been going door-to-door in swing precincts in this suburban Cleveland district; the city's ethnic groups have all moved outward along radial avenues, and all of them (except blacks) are represented in this district, which, like most congressional districts voted for Reagan in 1980 and for a Democratic congressman in 1982. Rep. Ed Feighan is confident he can hold the district, though he concedes Reagan is ahead, and expects the president to carry it; Hatchadorian insists he is in a position to win.

Districts such as this are keys to continuing working control of the House for Tip O'Neill's Democrats, just as large industrial bellwether states such as Ohio are keys to whether Ronald Reagan can keep the presidency out of reach of Walter Mondale.

The assumption on all sides now is that Reagan is well ahead in the 19th district and in Ohio. Sitting in his Republican Party chairman's office in Cleveland, an office decorated not only with elephants but with the history books he likes to read, Robert Hughes concedes that, "Yes, the presidential debate had an impact. The very appearance of Mondale brought him up 5 percent in the polls. I think Reagan's 10 points ahead in Ohio; it was 15 percent." But presidential elections are decided "by great moving forces." For him this is like 1956: "people are going to vote peace and prosperity. Why should we change?" Taking his reading glasses on and off, flicking ashes from his Camel, he says the debate actually hurt Mondale. "When he mentioned taxes, I turned to my wife, and said that finishes him."

The tax issue has a special resonance in Ohio. Democratic Gov. Richard Celeste, elected in 1982, raised state income taxes in 1983; only by adroit campaigning were his allies able to defeat an anti-tax referendum in 1984. Mondale's superior performance in the debate may have only helped him establish a position that isn't terribly popular.

But Ed Feighan says the debate "was a real help," and his campaign manager adds that now "at the Euclid Democratic Club they're starting to say that in the next debate Mondale could do it." The phones in local headquarters started ringing heavily Monday, and the number of volunteers increased "dramatically."

Yet Feighan's own ads have been personal (with his family on the beach) and have stressed local issues such as constituent service. Hatchadorian ads, in contrast, cover the central issues of the presidential campaign: jobs and economic growth, defense (the Reagan modernization) and taxes. Ironically, incumbents Reagan and Feighan are relying on ads that play off the voters' general optimism and good feelings; challengers Mondale and Hatchadorian present spiky, aggressive ads geared to specific issues. In 1982, Ohio voters were enraged about the state of the economy, and Reaganomics was a dirty word; Celeste beat a supply-sider with 60 percent of the vote. Now the Democrats are sidestepping the central economic issues.

Unemployment is still relatively high in Ohio; population is down; many of those who have left are accepting much lower wages than they would have a few years ago. But even if Reaganomics has not brought complete prosperity, it seems to have given voters a sense that things are back under control. Feighan's mid-September poll, which showed him ahead 55-25, also shows Reagan with a 52-32 lead in the 19th district. Hatchadorian's most recent poll, begun before the debate and completed the day after, shows similar presidential numbers; the Republicans won't give out the numbers on the House race, but say as many voters want a Republican as a Democratic congressman.

So both incumbents lead, but their percentages -- Feighan in the 19th, Reagan in Ohio -- are only slightly higher than 50 percent. Neither side is giving up on the race where it's behind.

That gives a certain tension to the remaining weeks of the campaign, a tension that was apparent in the crowd of 200 Republicans watching the vice presidential debate at the Howard Johnson Lakefront in Cleveland.

This wasn't a country club crowd: one in five were black, many working class, some Jewish. The Republicans cheered Bush from his first answer ("America is back") and booed Ferraro occasionally. Hughes laughed, got up to claim victory before local TV cameras. The consensus: a big Bush victory, a relief after Sunday night.

An entirely different verdict came from the 600 Democrats -- also a diverse, spirited crowd -- downtown at the Bond Court hotel. They dwelled on Ferraro's spirited response to Bush's condescension, her command of facts, and most of all her closing statement. "Sunday was a remarkable turnaround," Celeste said, "and Geraldine Ferraro sustained it." Each side genuinely believed its candidate won. Both did make good arguments. Bush made as good a case for his Central America policy as anyone has done. And Ferraro's close made as strong a plea for a more compassionate government as has been heard in this campaign.

In South Euclid, Walter Mondale already has a fair number of votes and may win more; but the issues he so successfully framed Sunday don't seem to be working strongly enough -- yet -- in this year of peace and prosperity. Reagan's poor performance, even after Bush's effort, makes it harder for Republicans to extend their strength on issues to the congressional level. Both Feighan and Hatchadorian are convinced that foreign policy issues -- the subject of the Oct. 21 debate -- favor them; Feighan cites the nuclear freeze and Central America; Hatchadorian supports the build-down and Reagan Central America policy and says Feighan is for "peace through weakness." Both sides are looking at the same electorate and seeing quite different things.

In Washington there may be scoffing at the candidates. In Ohio, registration, despite lower population, is at record levels; absentee ballot requests are pouring in; headquarters on all sides are buzzing with cheerful volunteers. There is an uneasiness in the air, a sense that the outcome -- the presidential race, the control of Congress -- is not yet determined.