CHICAGO -- Ronald Regan campaigned in politically crucial Great Lakes states today, acting more and more like a man who thinks he has already clinched the election.

While continuing to hammer away at President Carter’s economic record, Reagan seemed most enthusiastic when he talked about wanting to be president so he could “take government off the backs of the American people.” And in Pittsburgh, the Republican nominee stayed from his text to reflect on what had gone wrong with the administration he seeks to replace.

“We started with an administration that didn’t have any plan, any economic plan, of what they were going to do with the presidency other than enjoy it,” Reagan said. “And now we’re reaping this harvest, and I look forward to turning around some of the things that have gone wrong.”

What Reagan was trying to do in Illinois, Michigan and Ohio was to harvest usually Democratic blue-collar votes -- the consistent target of his personal campaigning in the Great Lakes states. Whenever he is near voters who might possibly be Democrats, Reagan likes to remind them that he came from that side of the political tracks.

On Thursday night, at a workingclass bar in Bayonne, N.J., Reagan said, “I know what it’s like to pull the Republican lever for the first time, because I used to be a Democrat myself, and I can tell you it only hurts for a minute and then it feels just great.”

Reagan’s innate caution is legendary with his own staff. He almost never predicts victory, and he has an athlete’s superstition about the evils of overconfidence. In California, near the end of his successful campaigns, he used to tell partisans, “President Dewey warned me not to get overconfident.” u

But Reagan is so happy now with the way he thinks things are going that he can scarcely restrain himself. He has told both aides and reporters that things are “looking good” in the campaign, and he seems more certain about Tuesday’s outcome than he has been at any time since the Republican National Convention in July.

Reagan strategists believe he will win New Jersey, which has gone Republican in presidential elections since 1964, but that he probably will lose Pennsylvania, where he campaigned Thursday night.

The Reagan campaign is upbeat about propspects in Illinois, where Regan campaigned today, and in Michigan and Ohio, where he is to campaign Saturday.

Reagan polls show the Republican nominee 6 points ahead in Illinois, 3 to 5 points ahead in Michigan and 2 points behind in Ohio.

“Two of these three give us the election, and we could win them all,” one Reagan strategist said.

Curiously, the Reagan campaign team is most optimistic about Ohio among this trio of states despite Carter’s narrow lead there. This is because the Reagan strategists believe that the Republican organization in Ohio is far superior and will produce a strong voter turnout on Election Day.

All of the internal reports on the reaction to Tuesday’s debate with Carter have been encouraging to Reagan and his aides.

Don Totten, Reagan political director in four midwestern states, said a poll taken in Illinois after the debate showed that three out of four undecided voters gave Reagan the debate edge.

At a rally in a high school in the Chicago suburb of Des Plaines, Reagan stuck to his basic attack on Carter’s economic policies. Speaking to a crowd dominated by teen-agers in a Halloween mood, Reagan said that a second Carter term would promise “more of the same -- more skyrocketing inflation, more high unemployment, more devastating interest rates.”

Earlier, as he left a downtown Pittsburg hotel, Reagan was told by a local reporter that the “FBI says Jimmy Carter is not cooperating fully” in the investigation of his brother, Billy. Reagan said in response that he favored more investigation and “a clear and open explanation” to the American people.

When he was asked whether Carter had provided such an explanation, Reagan replied, “Well, he does seem to be dragging his feet.”

Reagan finished another long day of campaigning in Wisconsin, a state Carter is expected to win. Before a large labor-oriented audience in Milwaukee, Reagan gave his economics message and then poked fun at Carter’s statement in the debate that he had asked his 13-year-old daughter, Amy, what the most important issue in the campaign was. Her response, according to Carter: the control of nuclear weaponry.

“I know he touched our hearts, all of us, the other night,” Reagan said of Carter. “I remember when Patti and Ron [his children] were little tiny kids and we used to talk about nuclear power.”