Early in a mostly satisfying sweep across the country this week, Ronald Reagan rose through the open roof of his bubbletop limousine as it slowed to a pre-programmed crawl to please the lunch-hour crowds along Gay Street in Knoxville, Tenn.

The candidate grinned the perpetual smile and waved the presidential salute, his body leaning first in a good-guy tilt to the right and then in an aw-gosh swing to the left.

But along Gay Street, as one of Reagan's caustic traveling companions observed, the madding crowds of the 1980 presidential campaign lined the way "sometimes one deep." The observation was kind. On Gay Street only casual strollers waved back, despite the front-page announcement that morning that the man who may become president would emerge from his bubbletop at precisely this moment.

Campaign '80 is that way, not peculiar to Reagan, but typical of the times.

"At least they waved to Reagan with a full hand," said Jim Brady, a campaign aide who has watched American politics evolve from the truly madding crowds of the '60s to the maddening frustration of empty sidewalks in the '80s.

As Reagan moved across the country to the West Coast, campaign advance men could crank up friendly crowds of Cuban Americans in Miami, Bible Belt believers in Springfield, Mo., and sagebrush rebellious westerners in Colorado who waved signs saying, "Don't Forget Us."

But without a strong single-issue prodding, whether it's the lingering dream of taking Cuba back from Castro or federal lands back from the Interior Department, people just don't seem to care.

In Fort Lauderdale, the security cops on rooftops outnumbered the people on Broward Boulevard as the strange spectacle of a presidential caravan swept by. At Baton Rouge, exactly 30 persons met the candidate at the airport gate. As the week neared an end and Reagan landed in the state he governed for eight years, the number was down to two dozen for an evening arrival at San Francisco International Airport.

In the wake of the televised debate with John B. Anderson, both the candidate's staff and his traveling press corps agreed that Reagan was drawing some of the best crowds of his presidential campaign.

But, in this turned-off year, the advance men have given up on trying to package more than one crowd to one town. Airport rallies have been abandoned unless that's the only stop. Sidewalk throngs are too tough to create -- even at noon -- and the goal is to stuff all the town's curious into one slightly too-small hall.

"Medium-sized halls are in great demand these days," said Brady. "It used to be that you went after the Hippodrome, but not this year."

This is a year without heroes. Americans are seeing would-be presidents as quite ordinary men, and they are seeing them often enough on small screens in the comfort of their living rooms.

Brady, who observed that Anderson was playing to near-empty halls just days after almost 50 million people watched the debate and that the advance men are having the same troubles when the true presidential presence moves out of the Rose Garden, recalls the good old days with fatalistic whimsy.

"I can remember bringing Nixon to Marion, Ill., in 1968, and we were worried that we had too many people -- 30,000 for an airport rally at a town whose population was just half that.

"That age is gone. Maybe it's because we're into a media age. They see enough of these guys on TV every night."

The candidates and their aides like to think that it is the nightly television exposure that is taking the spontaneity out of this election campaign. Others think it is the ordinary men. It's probably a little of both.

In Knoxville, as the Reagan entourage moved off almost empty Gay Street into a nicely compact downtown market square, a lunchtime crowd of perhaps 3,000 filled the carefully selected Campaign '80 arena almost perfectly.

The advance men had done most of the work in filling the square with friendlies who provided just the right backdrop for a midday event timed to be the highlight of the evening network news. The campaign pros also knew that lunchtime would inflate their best efforts with passersby taken hostage by the scene.

Morris Skalet came to the square this day not to see Reagan but to deposit his Social Security check in the bank.

Skalet is Reagan's age, 69, a retired Knoxville jeweler who watches a lot of television, thinks the Republican is a little too old and probably will vote for President Carter.

Standing on the sidelines, Skalet made it clear he wouldn't go out of his way, even to see the man he probably will vote for. But being this close, after his trip to the bank, he paused for a look-see.

He stood just 40 feet away from the man who was introduced, as he always is, as the next president of the United States.

But in the 1980-style crowd, Skalet found himself directly behind a mobile television van, leaving him no view of the candidate.

But he shrugged that off, figuring he could catch it on the 6:30 news instead.