In the opening days of this campaign, Democratic challenger Walter F. Mondale has taken out a tiny hammer and chisel and begun chipping away at the massive pedestal of patriotic pride and personal affection on which Republicans are building President Reagan's reelection strategy.

Tracking the president through California and other parts of Reagan's strong western base, Mondale did not "come out smoking" as his more enthusiastic handlers had promised in pre-Labor Day interviews.

Instead, he "came out poking," jabbing at Reagan on taxes, deficits, education and arms control.

The former vice president was probing for weak points he can exploit in the hoped-for debate later this month that his managers count on to focus voters' minds on the critical differences between the presidential candidates.

But while Mondale nipped at his heels, seeking physical proximity as a way of simulating and stimulating a national debate, Reagan barely deigned to notice.

The president turned his back on Mondale -- and on the negative, anti-Mondale rhetoric that dominated the Republican convention in Dallas -- saying, "We can forget the pack of pessimists roaming the land." He offered instead what he called "a sparkling vision of tomorrow."

To an observer shuttling between the two campaigns, the contrasts were almost all in Reagan's favor. He had bigger crowds, better organization and more powerful rhetoric. Most strikingly, Reagan seemed to hit the larger themes that drew a powerful, positive response from the late summer audiences in prospering, post-Olympic America.

By comparison, Mondale was talking to smaller crowds on more narrow, focused issues and drawing a response that seemed more often respectful than enthusiastic.

Mondale's chief media-and-message adviser, Richard Leone, said today, "We've begun to lay down the themes . . . on which we hope to build. We're not trying to get all the points of Reagan's lead back in one trip. We hope by October it's a race, and then people will focus on the issues we've established."

That reflects the conventional wisdom of a basketball coach whose team finds itself trailing a hot-shooting opponent by 15 points in the first quarter. "Don't panic. Don't press," is the advice in that situation. "Just play your own game."

But trailing Reagan through southern California, the Silicon Valley and the American Legion convention in Salt Lake City, Mondale resembled the youth of whom his mentor, Hubert H. Humphrey, often spoke, the one whose father was always saying, "Wake up, son, you're an hour late and a dollar behind the other boys."

Humphrey told that story in his 1968 campaign, when he was constantly and unavailingly playing catch-up to Richard M. Nixon. Mondale faces at least as large a task in overhauling Reagan, and his start was almost as stumbling as Humphrey's 16 years ago.

A bad scheduling decision sent Mondale down the Labor Day parade route in New York City hours before the crowd arrived. Sudden showers soaked a mid-day rally in Wisconsin. A microphone failure and a fainting woman in the crowd marred the evening rally in Long Beach, Calif.

On Tuesday, sloppy advance work forced Mondale to walk into a San Jose State lecture hall past a loud and jeering contingent of pro-Reagan campus Young Republicans. Hesitancy in his scheduling unit teed off American Legion officials before Mondale decided, late last week, to address their convention in Salt Lake City this morning. And this noon, an enthusiastic crowd wanting to hear Mondale speak had to endure a soaking from the first real rain in more than 60 days.

In contrast to the smoothly running Reagan campaign, the Mondale effort often looked as out-of-its-league as a kazoo band trying to drown out a mighty Wurlitzer.

The differences began with the physical and verbal sense the candidates themselves conveyed. Reagan dominated the stage with his size and the resonance of his voice -- easily recognizable and understandable even from the fringes of his vast Labor Day crowds.

The warm-up speakers at a Reagan rally were clearly that -- cheerleaders for the star. On the other hand, the hors d'oeuvres at the banquets the Democrats served up this week sometimes crowded out the the main course, Mondale.

In both Merrill, Wis., and here, vice-presidential nominee Geraldine A. Ferraro drew at least as many cheers as her running mate. And in Long Beach, the crowd seemed almost regretful when Sen. Gary Hart (D-Colo.) turned over the microphone to Mondale.

Reagan's entrances were theatrical, Mondale's almost invisible. Rather than trying to overcome these differences, Mondale's stage managers were trying to take what he gives them and turn it to an advantage. Tuesday they kept him in small groups and perched on a chair or standing slouched at the microphone, tie loosened, jacket off, shirt sleeves rolled up and answering questions -- something Reagan rarely does. The strategy seems to be that if they cannot show Mondale as a commanding figure, they will show him "up close and personal."

In certain respects, the strategy seems to be working. Reagan was plainly thrown on the defensive by Mondale's sharpshooting on the issue of religion-and-government.

The letters column of the Los Angeles Times on the day Reagan launched his campaign in his home state was filled with correspondence echoing Mondale's criticisms of the Dallas speech in which Reagan seemed to dedicate himself to spreading the Gospel.

By the time he got to Salt Lake City, the president was saying, "I can't think of anyone who favors the government establishing a religion in this country. I know I don't."

But for the most part, Reagan talked this week as a man who feels the current of public opinion -- if not of history -- is on his side, leaving Mondale to the less attractive and inspiring role of skeptic.

In his future-oriented kickoff speech in Irvine, Reagan said, "The space shuttle Discovery circles the Earth this very moment, reminding us that America has always been greatest when it does not shrink from greatness." At San Jose, Mondale fretted that cutbacks in basic science grants could mean that "Europeans are getting the jump on us in high-energy research."

In Compton, Calif., Mondale pulled out charts and bar graphs to argue that Reagan's tax cuts had benefited the rich more than the poor. In Cupertino, Calif., Reagan said he just wanted to "bring everyone's tax rates down, not up," because "we believe in high-tech, not high taxes."

At the Legion convention, Reagan asserted that his defense buildup has given "America's military forces . . . better people . . . better equipped, better armed, better trained" than ever before. Mondale came along a day later saying that Reagan has fouled up because "procurement of strategic nuclear forces has grown three times faster than for conventional arms."

It was Reagan's message that seemed to touch the responsive chord. Mondale aides conceded their candidate was using this week to test-market his campaign talks. "We didn't come out smoking," one said, "because we don't yet know what will light a fire."

Mondale repeatedly said that the November results will show "what kind of a people we are." The people he and Reagan saw this week looked more contented than concerned.

Bob Boulding, a Long Beach barber who attended the first Reagan rally, said it seemed to him that "Mondale is searching for ways to do things Reagan has already achieved -- giving everybody an equal chance and building a better country for everyone."

Dave Talamantes, 28, a maintenance man who turned out to hear Mondale in Compton, said, "Four years ago, I didn't vote for Reagan. I thought he was just a Hollywood actor. But he's shown a lot of backbone in that job."

Mondale seems to recognize what he is up against. At the Merrill rally, he reminded his audience that when John F. Kennedy started his 1960 campaign, the Republicans accused him of being a spoilsport, spreading worry in a country enjoying President Dwight D. Eisenhower's benign leadership. Kennedy's response, Mondale recalled, was, "This is a great country, but I think it can be a greater one."

A reporter who traveled with Kennedy that first week of the 1960 campaign, through many of the same western states Mondale has just visited, remembers that the Kennedy message did not begin to catch on until Kennedy confronted Nixon in their first televised debate. A similar debate seems to be Mondale's best hope of making this a race.