President Carter, conceding that his sharp attacks on Ronald Reagan were a mistake, said last night that he plans to tone down his rhetoric and change his tactics in an effort to get his reelection drive "back on the track."

Reflecting a mid-campaign reassessment by his political advisers, who are frustrated by the direction of the campaign, Carter said that he will try to refrain from "personal" references to his Republican opponent and will shift the emphasis of his campaigning to a series of major addresses on the issues.

In an interview with Barbara Walters on ABC News, the president said he will make a series of broadcast speeches on major issues, beginning with a radio address Sunday on the economy, and will devote more of his campaign time in the remaining four weeks to "major addresses" on such subjects as "defense, security, peace, arms control."

"I'll try to express myself clearly on the issues and try to be sure that we do not have a lowering of the tone of the campaign," he said.

In response to a question, Carter acknowledged that his increasingly strident assaults on Reagan have been a mistake.

"Yes, I'll say that, but there is enough blame to go around, and I think the press has failed sometimes to cover major issues," he said. "Mr. Reagan has made some comments about me that probably are ill-advised. I've made some about him that are ill-advised, and I'd like to get back on the track."

Campaigning Monday in Chicago, Carter warned that the election of Reagan would divide "black from white, North from South and Jew from Christian." Before that, he had told a California audience the election would decide "whether we have peace or war."

Earlier yesterday, White House press secretary Jody Powell hinted at the coming shift in the tone and tactics of the Carter campaign. He said that in recent days the president's political strategists had made some fundamental decision on how to focus the campaign "on the very real differences between the candidates and the substantive nature of those differences."

The shift reflects a decline in confidence among Carter's campaign advisers. Surveys now show the president running behind his GOP opponent, particularly in projections of electoral votes. Moreover, it has become increasingly clear that Carter's attempt to portray Reagan as a dangerous political extremist who might plunge the country into war was not working and in some cases had backfired.

Privately, many Carter aides, who in 1976 bitterly assailed the White House press corps for giving "a free ride" to then President Ford, are at least as bitter this year about the press coverage of Reagan.

In the interview, Carter conceded that his rhetoric may have been excessive at times, but he said this resulted from his deep feelings and "human nature."

"Some of the issues are just burning with fervor in my mind and in my heart and I have to sometimes speak extemporaneously and I have gotten carried away on a couple of occasions," he said.

The president also showed some frustration over press coverage of the campaign. Citing what he called Reagan's proposal to "abandon" the pending strategic arms limitation treaty with the Soviet Union and to "launch a nuclear arms race," he said:

"This is a shocking and very profound departure from the policies of all presidents and of this nation since Truman was in office. I watched with great attention that evening to the news broadcasts. ABC did not mention it. CBS did not mention it. NBC did not mention it. . . . And in my commitment to make that issue strong and to express the importance of it , I maybe went to excess. I'll accept the responsibility for that. But I'll do the best I can in the weeks ahead not to repeat that kind of personal involvement of the candidates in the race."

Carter said he still believes he has "a good chance" to overtake Reagan in the final weeks of the election. Voters have not yet focused intently on the race and "there is still a very large undecided group," he said.

The president leaves today on a two-day campaign trip to Tennessee, North Carolina and Florida. His aides said the first evidence of the change in tone and approach of the campaign will become clear during the trip.