White House national security adviser Richard V. Allen announced yesterday that he is taking an administrative leave of absence from his job until the Justice Department completes its investigation of his receiving $1,000 from Japanese journalists who had interviewed Nancy Reagan.

Allen conceded, in a nationally televised appearance, that he had exercised "bad judgment" but had done nothing illegal in the affair, which has made him a center of controversy for the past two weeks. But he maintained later, in a lengthy interview with The Washington Post, that he would eventually be vindicated and back on the job because "it was only a one-time bad judgment."

In his wide-ranging interview with The Post, Allen provided new details concerning the arrangements for the interview and his other contacts with his long-standing friends from Japanese industry.

Allen said that his involvement in the interview began back on Dec. 7, 1980, the 39th anniversary of the bombing of Pearl Harbor, when he was first asked to arrange the interview during a telephone call from Tokyo from his longtime friend, Tamotsu Takase, a Japanese business consultant.

Takase had called to ask Allen to make arrangements for himself, his wife, and others to receive invitations and tickets to the Reagan inauguration, Allen said. And during the conversation, Allen continued, Takase "asked if his wife could conduct an interview with Mrs. Reagan for a housewives' magazine."

There was never any mention of money in that conversation or any subsequent conversation, Allen said.

Allen also said, in yesterday's interview with The Post, that while he later met three or four times with Takase at the White House, he never discussed business matters in those conversations. He specifically repudiated quotes that Takase reportedly passed on to Japanese executives as business advice from Allen. Takase had made the remarks in a speech in Japan after returning from a White House meeting he and an official of the Toyota auto company had with Allen.

"That's Takase talking and not me talking," said Allen. "I don't recall ever saying that to Takase."

And Allen also acknowledged that he had lunch twice in the White House mess with Yasuhiko Suzuki, Washington vice president for Nissan U.S.A., the Datsun marketing company that kept Allen on an annual retainer before Allen assumed his White House job. But Allen said those lunches were "purely social" and that no business was discussed.

Allen has been criticized within the White House inner circle for his actions not only for receiving the $1,000 and then failing to turn it over to authorities, but for his contacts while in the White House with his friends from his days as a consultant to several Japanese businesses.

There had been published reports that presidential chief of staff James A. Baker III, deputy chief of staff Michael K. Deaver, and Nancy Reagan believed Allen should be replaced as national security adviser for having exercised bad judgment.

Only White House counselor Edwin Meese III, among the President Reagan's top advisers, was reportedly urging that Allen remain in his post while the Justice Department continues its inquiry to see whether a special prosecutor should be appointed to fully investigate the case.

According to a White House spokesman, Allen telephoned Meese Saturday to tell him that he had decided to request administrative leave until the matter is fully investigated, and that Meese then telephoned the president at his ranch in Santa Barbara, Calif., to relay the message.

At 8:19 p.m. PST, Allen telephoned the president and formally informed him of his decision. Asked if Allen will return to his job if he is vindicated by the Justice Department inquiry, deputy press secretary Larry Speakes responded that he has "no reason to think otherwise."

For now, Allen's duties will be assumed by his deputy, James W. Nance, a retired admiral. Previously, Nance served as an aide to now-Secretary of State Alexander M. Haig Jr., back when Haig was commander of NATO forces.

Allen announced his decision on the television show "Meet the Press" (NBC, WRC), after agreeing to appear only the day before.

"The interest in this case has developed to an extent where great pressures have been brought to bear on the White House," Allen said on the show. "In recognition of this, I have spoken with the president yesterday, requested that he grant me administrative leave until such time as the Justice Department has completed its investigation. At the conclusion of that investigation, I expect the facts will be fully known and that I fully expect to resume my duties."

He also said: "It's time that this case be aired in a responsible forum, and that it not be made on the basis of innuendo and sly allegations . . . . This allows me now to speak out."

Allen said that at no time had Baker or Deaver or Mrs. Reagan or anyone else urged him to leave his national security post.

In his interview with The Post, Allen expanded on his television remarks.

Allen said he originally understood from Takase that Takase's wife, Chizuko, would conduct the interview but it turned out that she just helped arrange it and acted as interpreter.

The day after the initial contact, Dec. 8, Allen wrote a two-paragraph memo to Reagan's scheduling director, Charles Tyson, later an Allen staffer on the national security council. A copy was sent to Mrs. Reagan's press secretary at the time, Nancy Reynolds. Allen said that he wrote that he was "loath" to add any events to the schedule, but that he hoped the request for the interview could be favorably considered.

Allen said in yesterday's interview, that "at some point . . . I don't remember when" he asked former Reagan aide Peter Hannaford, to whom Allen was selling his Potomac International consulting business, to help the Japanese arrange the interview with Mrs. Reagan.

According to reports from Tokyo, the representatives of the Japanese magazine had decided to give Mrs. Reagan a $1,000 honorarium for the interview, but Allen said neither Mrs. Takase nor her husband nor anyone else ever mentioned the money to him.

Allen said that the magazine representatives finally met with Mrs. Reagan in a confused, five- to seven-minute session, on Jan. 21, in the foyer of the White House as the Reagans were walking downstairs to a reception. There were photographs and about three questions, he said.

One of the Japanese women, he believes it was Mrs. Takase, thrust some papers toward Mrs. Reagan and Allen said he intercepted them.

They included a copy of the magazine and copies of interviews of former first ladies Patricia Nixon and Rosalynn Carter. There was also an envelope which had on it some Japanese lettering and a floral design.

Months later, when found in an Executive Office Building file cabinet, the envelope also had a written notation that could be read as either $1,000 or $10,000, he said.

But Allen says firmly that there was no such notation on the envelope when he received it and he says others who handled it since back up his story.

Allen says he left the White House residence area and walked to his office in the Executive Office Building next door.

There, he says he first looked inside the envelope and saw that it contained cash. He counted ten $100 bills.

He says he walked into his office and handed the envelope to his secretary, Irene G. Derus, telling her with surprise that the Japanese had tried to give Mrs. Reagan cash.

He said now-Secretary of the Navy John F. Lehman Jr. heard him tell Derus, "Put it away. We'll have to turn this over to the White House counsel or the gift unit . . . ."

She put it in a file drawer that has a combination lock--Allen said he never had the combination to it.

A couple of weeks later, Allen said the envelope and other papers were moved by Col. Donald Johnson, then an NSC military aide, to another locked file cabinet in the adjacent office, Room 375, which Allen used as a hideaway office.

Allen said he forgot about the money, which was discovered by aides who moved into Room 375 in September. They reportedly notified Meese of the money and he notified the FBI.

Allen said he was never contacted about it by Meese, and he knew nothing of the investigation that had begun until FBI Director William H. Webster phoned him in late September.

Allen also said yesterday that Hannaford had in recent days paid in full the debt, believed to be approximately $50,000, owed him for the sale of his consulting firm.

Allen also denied as "absolute rubbish" a Japanese newspaper report that Takase had given Allen "a big gift" in Washington on Jan. 18, three days before the interview occurred.

Allen said Takase telephoned him that day to say that he had arrived in town and was at his hotel, but that Takase never gave him any gift, nor passed on any information of a business nature.

The author of the magazine article maintained that she intended to give Allen just one of the women's Seiko wrist watches he received but that when asked he said he would take both.

Allen said he was given the watches by Mrs. Takase, an old friend with whom he often exchanged gifts.

He said both were given him before inauguration day, and that he didn't know Mrs. Takase had not bought them herself.

Allen said one of the watches is still in the box it came in, the other was given to one of his daughters "to wear for a special occasion," and has been lost CAPTION: Picture 1, RICHARD V. ALLEN...concedes "bad judgement."; Picture 2, Allen, with his wife, Patricia, and other family members, arrives for TV interview about receiving $1,000 from Japanese journalists who had interviewed Nancy Reagan. AP