Alfred Bloomingdale, 66, a close friend and adviser of President Reagan and the founder of the Diners Club credit card company, died of cancer Aug. 20 at St. John's Hospital here.

Mr. Bloomingdale, a member of the president's "kitchen cabinet," and his wife, Betsy, whom he married in 1946, often visited the Reagans at the White House and hosted them at their California home.

A White House spokesman said that the Reagans were informed of the death upon their arrival at their Santa Barbara ranch Saturday, but that they had no public comment.

Last month, Mr. Bloomingdale and his wife became the target of a "palimony" lawsuit filed by a woman who claimed she had been promised lifetime support by Mr. Bloomingdale during their 12-year love affair.

In the lawsuit, Vicki Morgan, who said she had been Mr. Bloomingdale's companion since she was 17 years old, sued him and his wife for $5 million each. She claimed that although she never had a live-in relationship with the businessman, he was a "second father" to her son by another man. She said she gave up other job opportunities to serve as Mr. Bloomingdale's "traveling companion, confidante and business partner."

Miss Morgan also contended that Mrs. Bloomingdale forced her husband to end the relationship.

Born in New York City, Mr. Bloomingdale was the son of Hiram C. Bloomingdale and grandson of one of the two brothers who founded the Bloomingdale's department store.

He was a 1938 graduate of Brown University, where, he once told a reporter, he spent much of his time playing football. After graduation, he joined the family business. But almost immediately he began a career in show business as a Broadway and Hollywood producer and agent.

In the 1940s, he produced 20 Broadway musicals, including "Ziegfeld Follies," starring Milton Berle. He ran a New York shipyard during World War II and produced shows for the armed forces. He then opened a talent agency. His clients included Frank Sinatra and the late Judy Holliday.

In 1951, Mr. Bloomingdale founded the Diners Club with an associate, Ralph Schneider, and was sometimes known as the "father of the credit card." Mr. Bloomingdale served as Diners Club president and chairman.

During the 1970s, he was active in real estate ventures in California, Florida and Georgia.

He was a trustee of Brown University and a regent of Loyola Marymount College in Los Angeles. He also was a director of the International Rescue Committee.

In addition to his wife, survivors include two sons, Lee Geoffrey and Robert Russell, and a daughter, Elizabeth Lee (Lisa), and four grandchildren.