President Reagan tried today to ward off Republican overconfidence in the home stretch of the 1984 campaign.

Responding to weekend polls showing him with a commanding lead over Democratic candidate Walter F. Mondale, Reagan repeatedly warned his supporters against complacency in a day of campaigning in southeast Pennsylvania and West Virginia.

On the steps of the Delaware County Courthouse here, Reagan exhorted a crowd of more than 15,000, sprinkled with a few protesters:

"I've been trying very hard not to read the polls, and don't you read them. President Dewey told me never to become overconfident," Reagan said, alluding to Republican presidential candidate Thomas E. Dewey, who lost the 1948 election to President Harry S Truman.

"Get out the vote. Tell your neighbors to get there to vote. Don't anyone say, 'Well, I'm not needed, not necessary,' and stay home."

Reagan added, "I know of elections that were lost by less than one-half a vote per precinct in this country. Turn out and vote."

He also made a special effort to recognize GOP congressional candidates. He joined one, Curt Weldon, who is challenging Rep. Bob Edgar (D-Pa.) here, in a victory salute, and asked voters to make Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) "unhappy" on election night.

"I hope to win a second term," Reagan said, "but I'll tell you quite frankly that if a gypsy looked into her crystal ball and said, 'You can win this election with a lot of votes or win by just a few votes and get a sympathetic Congress,' I would choose the latter, a sympathetic Congress . . . . And if you can, well, win those races for the Gipper."

Reagan intensified his get-out-the-vote appeals even though his polls show him leading Mondale by 15 percentage points. One senior adviser said Reagan has "good reason" to worry about turnout Nov. 6 if voters conclude that the race is over.

"Tell 'em it's over!" shouted one exuberant backer as Reagan spoke here. Asked later if he were headed for a landslide, Reagan replied: "I'd be scared if I thought that. I'd scare myself for even thinking that."

However, many Reagan aides were exceedingly confident, saying he is running ahead of Mondale in every state but Minnesota, where their polls now show a draw. "A lot of guys have lost elections because of overconfidence," said another aide, "but it's hard to see how Mondale takes advantage of it."

Responding to Mondale's charge over the weekend that the president was so confident that he was sleeping at Camp David as the presidential campaign reaches a climax, Reagan said: "Well, if I hadn't been overnight at Camp David, I would have been overnight at the White House, and either place is good sleeping."

As Mondale seemed to be returning to basic principles in the final week, so was Reagan. Aides said this was one reason for a new passage in his stump speech today recalling the "killer inflation" in energy, food and housing prices during the Carter administration.

Reagan said President Jimmy Carter had used five economic plans "and nearly tripled inflation. By contrast, we trusted the people, and with just one economic program we cut inflation by two-thirds."

"So you can see that when we analyze what he [Mondale] has said in this campaign, our biggest concern is not whether he will forget the past, but whether he's going to bring it back."

Asked to comment on Mondale's themes that the president's policies are unfair and that he has done little to bring about arms control, which the Democratic nominee has stressed recently, Reagan responded: "You could say, 'Well, what's new about that?' Even some of you have been saying that for so long. But I'm not going to believe it, because I know it isn't true."

On foreign policy issues, Reagan recited abuses by Nicaragua's Sandinista governmemt and asked, "Don't you think it's time my opponent stood up, spoke out and condemned these Sandinista crimes?"

Reagan, who in the past has made frequent reference to President John F. Kennedy in his appeals to Democrats, today dropped the use of Kennedy's name and referred only to Democratic President Truman. It was disclosed last week that Reagan had written a letter critical of Kennedy during the 1960 campaign and sent it to Richard M. Nixon.

Also today, Reagan brushed off editorial endorsements of Mondale by The Washington Post and The New York Times, saying, "What's new about that?"