Japanese writer Fuyuko Kamisaka said today that much of a controversial article she wrote on Nancy Reagan for a Japanese magazine last winter was based on material telexed later by an unidentified person at the White House.

Kamisaka today published a defense of her role in the affair, for which the magazine paid a gratuity that it said was intended for Mrs. Reagan. The $1,000 gratuity was later found in a safe used by Richard V. Allen, the national security adviser, who said he had forgotten about it after helping arrange the meeting between Mrs. Reagan and the writer.

Kamisaka angrily rejected allegations that she had not actually interviewed the first lady on Jan. 21, the day President Reagan took office. Mrs. Reagan has said, through an aide, that she does not remember giving the interview to journalists from Shufu no Tomo (Housewife's Companion) and had only a "faint recollection" of a photo session with them.

In a three-page article appearing in the Dec. 4 issue of Shukan Asahi, a weekly magazine, Kamisaka wrote that Mrs. Reagan's version of events was "something unthinkable. . . . I cannot let her statement pass."

Kamisaka wrote that she had used telex answers from the White House to questions submitted before the meeting with Mrs. Reagan to compile her report. An autobiography of the first lady was also used to augment her material, she wrote.

That was necessary, she explained, because the White House would not permit the use of a tape recorder or the services of a professional stenographer during the session.

A senior spokesman for the Shufu no Tomo magazine, who did not want his name used, suggested today that the interview took the form of a few hurried questions rather than a formal interview session and that the article was compiled largely from answers received later by telex.

After the interviewing team returned to Japan, he said, the magazine received responses to the bulk of its questions over its office telex. He said the company now has no record of the telex and he said he does not know who answered the questions or sent them from the White House.