White House national security adviser Richard V. Allen accepted two watches valued at about $340 from the same Japanese interviewers who gave him $1,000 intended for Nancy Reagan as a thank-you fee for an interview with her.

Allen, according to administration officials who spoke with him yesterday, admitted receiving the Seiko Quartz watches, but said both were given to him before he became a White House official Jan. 20, when there was no bar to his accepting gifts.

The author of the interview, Fuyuko Kamisaka, however, told Japanese reporters that one watch was given to Allen on Jan. 21, after the interview with Nancy Reagan.

By her account, she purchased both watches at Narita International Airport Jan. 15 on her way to the United States. On Jan. 16, the interviewers met with Allen at one of the offices he was using before entering the White House and gave him a gold-colored Seiko Quartz watch valued at about $170, according to the report, which first surfaced in the Japanese newspaper Mainichi Shimbun.

Five days later, after Allen had assumed his duties in the White House and on the day the Japanese reporters met briefly with Mrs. Reagan for a photo session and interview, Allen was asked whether he liked the gold watch or whether he wanted to exchange it for a silver-colored Seiko of the same value, according to the report.

The offer was reportedly made by Chizuko Takase, wife of Tamotsu Takase, a longtime business colleague of Allen. Allen reportedly told her that he liked the gold watch, but would also like to have a silver watch to give to an unidentified other person.

The timing is important because there is no legal obstacle to a private citizen accepting a gift, while a White House official is barred from accepting any gift worth more than $50.

Allen declined to comment on the watches yesterday, but the officials who spoke with him said he described the watches as gifts for his wife from a friend of many years, Mrs. Takase.

Allen reportedly was preparing to make a statement about the watches today.

There was no White House official comment on the watches last night, nor any explanation of why the watches had not been mentioned by Allen earlier. The disclosure of the gift of watches was the latest in a string of developments forcing Allen and his White House defenders to amend or amplify earlier statements.

The White House has taken to issuing statements in Allen's name rather than with the full backing of the White House, and appeared to be losing confidence that his explanations are the last word, since many unanswered questions remain.

The watches were the third gift reportedly passed from the Japanese to the Americans in connection with the Jan. 21 interview. Allen has said he intercepted an envelope containing $1,000 meant for Mrs. Reagan, put it in a safe and forgot about it for eight months. Mrs. Reagan received a lacquered stationery box, which she immediately turned over to the government archives, according to White House officials.

Meanwhile, sources said the FBI plans to interview former Reagan aide and speechwriter Peter D. Hannaford, who has said he met the interviewers, Mrs. Takase and Kamisaka, in Allen's office on Jan. 16. Hannaford acquired Allen's consulting firm, Potomac International Corp., two days later.

The FBI also plans to interview others, the sources said, but prosecutors have not yet asked agents to interview Mrs. Reagan.

Sources also said that, during the initial round of interviews with White House personnel, the FBI received reports that the cash given to Allen amounted to substantially more than $1,000. The sources said that these reports could not be substantiated, however. Presidential counselor Edwin Meese III, asked if he had heard that the amount was greater than $1,000, declined to comment.

White House officials also had no comment on reports of Allen's continued ad hoc meetings with former clients after taking his White House job, but they were known to be asking Allen to detail his contacts with Japanese businessmen.

Allen has not taken questions from reporters as new details of his actions in relation to the interview and in relation to Japanese automobile company executives have become known.

Instead, the White House has been taking questions to Allen and, in a series of meetings between Allen and other White House officials, written responses have been drafted and made available to reporters.

In the most recent of these, Allen conceded that he attended a March 24 meeting with President Reagan, Secretary of State Alexander M. Haig Jr., Masayoshi Ito, then the foreign minister of Japan, and others at which Japanese auto imports were discussed. Allen had said at the outset of administration discussions of auto import questions that he would not participate because he had been a consultant at $100,000 a year for Nissan U.S.A., the Datsun marketing arm in this country.

Allen said he checked his records and found he attended the meeting "as a notetaker" and did not speak.

It also was learned that Allen attended a March 20 meeting with Reagan, former Japanese prime minister Takeo Fukuda and others.

In addition, Allen recalled, after a question on the subject was asked, that he had provided a background briefing on auto imports in the White House press secretary's office.

In reaction to pubished reports that some senior Reagan advisers are urging the president to oust Allen, White House deputy press secretary Larry Speakes was asked whether the president still has confidence in Allen. "I have not heard him express otherwise," Speakes said.