WASHINGTON (AP) _ A mink coat once owned by Eleanor Roosevelt - about the time Richard M. Nixon was bragging about his wife's Republican cloth coat - was eagerly bought up Friday at a Democratic women's club bazaar for $530.

The three-quarter length brown mink, bearing an elegant ''ER'' monogram on its black lining, was donated to the fund-raising bazaar at the Woman's National Democratic Club by the late first lady's granddaughter, Eleanor R. Seagraves, a club member.

The coat's new owner is Doris Foster, a longtime party contributor and former volunteer for the Adlai Stevenson and Hubert Humphrey presidential campaigns who said she has always admired Eleanor Roosevelt for her liberal principles.

''She's been an idol of mine all my life,'' said Mrs. Foster, who beat everyone else to the coat rack and snatched up the Roosevelt mink as soon as the club's doors opened at 10 a.m. EDT.

After paying $500 plus $30 tax, the wife of retired State Department official Schuyler Foster happily modeled the coat and posed for her picture- taking fellow shoppers.

Mrs. Seagraves said she believed her grandmother bought the mink in the 1950s while she was living in Manhattan, after the death of her husband, President Franklin D. Roosevelt, in 1945.

About the time Mrs. Roosevelt purchased the mink, Nixon made his famous ''Checkers speech'' in September 1952 in response to charges that he was the beneficiary of a secret Republican slush fund. Nixon's televised defense was credited with keeping him on the GOP ticket as Dwight D. Eisenhower's vice presidential running mate.

During the speech, Nixon said at one point: ''I should say this, that Pat doesn't have a mink coat, but she does have a respectable Republican cloth coat.''

Mrs. Seagraves said she inherited her grandmother's mink from her mother, Anna, the oldest of Franklin and Eleanor Roosevelt's six children and their only daughter, who died in 1975.

Mrs. Seagraves, 62, wife of a Washington newsletter publisher, said she kept the coat in her bedroom closet along with another, full-length mink that also belonged to her namesake, but she never wore either one.

''I don't wear furs,'' she said. ''They are not my style. But if it can be used by someone who is devoted to ER, it should be.''

Mrs. Foster said she would wear her new mink ''on very choice occasions'' and eventually would donate it to the Eleanor Roosevelt museum at Val-Kill, the former first lady's home at Hyde Park, N.Y.

''Mrs. Roosevelt was the role model for my generation and for every generation since,'' Mrs. Foster said. ''The principles she stood for - Social Security, the minimum wage, housing and human rights - are what I want to see carried out.''

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