The 1980 presidential campaign was previewed in the capital city of Ohio on a perfect late-spring noon today. All of the publicity and organization that the campaigns of Jimmy Carter and Ronald Reagan could mobilize went into the nationally heralded "battle of the crowds."

And together, these mighty machines turned out about one-sixth the number of people that Ohio State's football team draws for a nonconference opponent on a rainy Saturday at the start of the hunting season.

Police estimated that 7,000 people were in Nationwide Plaza, the square in front of an insurance company office tower where the president spoke. And 5,000 to 6,000 were estimated to be on the lawn of the state capitol, where the prospective Republican nominee appeared.

The insurance company turned out its 4,500 employes to help swell the Carter crowd, and union construction workers were sent from a convention center project across the street.

Republican Gov. James A. Rhodes emptied the state office building for Reagan, some downtown business firms "encouraged" employes to attend and former Ohio State football coach Woody Hayes joined Reagan on the steps.

But both crowds were more interested in gawking than in cheering, and the prevailing mood was capsuled by real estate broker Jim Ryan, one of the dozens who did the tourist bit at both rallies without bothering to listen to much of what either man said.

Asked whom he was inclined to support, Ryan said, "I don't know enough about Reagan to make that decision. I supported President Ford last time, and I think it's a shame he wasn't elected, because he had the experience.

"Carter has been doing as good as anyone can with the issues as complicated as they are," Ryan said. "He's got the experience now, but it's sure cost us all a lot of money to get him educated."

That same reluctance and ambivalence showed up in a poll of 320 Franklin County (Columbus area) voters taken this month by Ohio State University students and published this morning by the Columbus Citizen Journal.

It gave Carter 36.6 percent and Reagan 35.3 percent, with 14.6 percent for independent John B. Anderson, who has filed a court suit seeking access to the Ohio ballot. Political scientist John Kessel, the professor who supervised the poll, characterized the responses this way:

"I can't remember an election with two such unpopular candidates."

The closeness of the race in this area was also reflected in a statewide poll published this week by the Gannett News Service. It had Carter and Reagan tied at 37 percent each in Ohio, with the remainder undecided. Carter carried Ohio by only 11,000 votes in 1976.

Today's twin rallies gave some clues to the preoccupations and strategies of the major party rivals at this stage of the campaign.

Carter was introduced by Ohio Sen. John Glenn, who appealed for support from backers of Carter's Democratic challenger, Sen. Edward M. Kennedy (Mass.).

Conceding that "there have been disappointments, of course," in Carter's conduct of the presidency, the old friend of the Kennedy family nonetheless said the time has come "to concentrate on those issues which unite us, instead of belaboring those that divide us. I say the time to unite is now."

Reagan was introduced by Rhodes, a longtime political ally of the late Nelson Rockefeller who switched his backing from John B. Connally last month. In his usual direct fashion, Rhodes laid out the essence of Reagan's strategy.

"We're trying," he said, "to get the Republicans under one umbrella. We're trying to get the independents to come with us. And we're trying to get the Democrats who are dissatisfied with what the present administration is taking out of their pocketbooks."

Predictably, Reagan's recital of the economic, military and diplomatic history of the past three and a half years was one of continuous decline, while Carter's view of the same period was of a nation "turning the tide" against adversity.

Predictably, too, Carter as the incumbent pretended lofty disdain of his challenger's presence, taking no notice in his remarks of the rival rally four blocks away.

Reagan, the showman, used Carter's visit to give his own familiar speech a new line.

"Somebody said they were having trouble telling which was his motorcade and which was ours," Reagan remarked. "You can tell his. It turns left at every corner."

But jokes aside, in both audiences the differences were being weighed carefully by some people -- among them, two black men.

"I came down here," said Arthur Cooper, a 51-year-old truck driver for a construction company who took the morning off to see Carter, "because I'm living better now than I ever did. I think he's doing a wonderful job. Even with inflation, I'm making out better than I ever did."

But Cecil Jones, 28, walked the four blocks from his job as a data processing manager at Nationwide Insurance, leaving the site of the Carter rally to hear his candidate, Reagan. "I think he'll bring some new ideas," Jones said. "Carter's a nice guy, but he's ineffective. He's not a good manager. Reagan had a surplus when he was governor of California, not the deficits we have now."