Former Reagan adviser Richard V. Allen confirmed last night that he received several "innocuous" excerpts of Carter National Security Council staff reports during the 1980 campaign. But he said it had been "unethical" for his campaign colleagues to have used a debate briefing book prepared for President Carter.

"The briefing book should have been returned, I think," Allen said on ABC's "Nightline" television program. He said it was "highly unethical to use it" and that Ronald Reagan would not have wanted it used.

Allen confirmed a report in The Washington Post last week that he had received parts of daily staff reports allegedly prepared for Carter's national security adviser, Zbigniew Brzezinski, during the campaign. The material, he said, "came in over the transom . . . totally unsolicited." He said he knew who his source was within the Carter administration, but that he would only provide this information to a "properly constituted authority." He said the material was "probably the most innocuous . . . I'd ever seen."

The FBI is investigating how Carter White House documents wound up in the possession of Reagan's 1980 campaign advisers.

In Santa Barbara, Calif., where President Reagan is vacationing, his aides announced yesterday that he has no objection to the FBI's interviewing administration officials and is ordering staffers to assist investigators in the debate book probe.

Reagan said last week that he would be willing to talk to FBI investigators. In response to questions, presidential spokesman Larry Speakes said yesterday: "The president has asked everyone to do everything possible to help the FBI with its investigation."

Speakes said Reagan has not received any indication of widening involvement by his aides, nor has he had any offers of resignation from staff members over the weekend.

In reply to reporters' questions, Speakes added that Reagan retains "full confidence" in administration officials in the debate book case, specifically White House chief of staff James A. Baker III, communications director David R. Gergen, CIA Director William J. Casey and Office of Management and Budget Director David A. Stockman.

Over this four-day holiday, White House aides have played down, if not ignored, the controversy that was preoccupying them when they left Washington.

Allen, who became Reagan's first national security adviser, was investigated by the FBI after an envelope with $1,000 he received from Japanese journalists was found in a safe in his former office. Allen said he meant to return the money and was cleared when probers found he had broken no law. He resigned last year.