The cause was complications from colon cancer, said a sister, Jeanne Straus.
Ms. Straus — her first name was pronounced Dee-Ann — was a scion of a wealthy family that built an innovative radio empire in Manhattan, where her father's station WMCA was credited with helping to popularize rock-and-roll in the United States and with broadcasting some of the first on-air editorials and political endorsements.
Like her father, Ms. Straus mixed business and politics, although for years she focused primarily on the former. She ran a catering company out of her 18th-century home in Bedford, N.Y., serving chutneys and bacon-wrapped watermelon rinds to the cocktail party set in Westchester County; served as publisher of her husband's New York-area newspaper chain, Trader Publications; and edited a high-end gossip magazine called the Westchester Wag.
"John Cheever would have railed against it," a reporter for the New York Times wrote in 1999, shortly after the publication's founding, "but probably would have studied the party pictures first."
Meanwhile, Ms. Straus developed an unusual talent in platform tennis, a cross between squash and tennis in which players volley on a raised platform surrounded by chicken-wire walls. She won 29 national championships, including several seniors titles in her 60s, and was inducted into the Platform Tennis Hall of Fame in 2004.
That year marked the beginning of a new professional focus for Ms. Straus. She left her job as group publisher of Manhattan Media, a chain of New York glossies, to work for the man she called "the Gov" — presidential candidate Howard Dean, the former Vermont governor and a close friend from their days at Yale.
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The campaign fizzled but sparked what Jeanne Straus described as her sister's "remaking." She was named president and publisher of the Washington-based American Prospect in 2005, and three years later became publisher of the Washington Monthly, founded in 1969 by editor Charles Peters.
Both publications mixed left-leaning policy analysis with early investigative work by journalists including Jonathan Chait and Ann Friedman at the Prospect and Michael Kinsley and Katherine Boo at the Monthly.
The magazines also were known for their long-standing financial woes, which Ms. Straus — while heading the Prospect — tried to ease by merging their publishing operations, according to Jeffrey Leonard, a private-equity manager who served on the Prospect's board.
The merger fell through, but Ms. Straus's budding interest in the Monthly — a publication that appeared on the verge of collapse after the departure of its publisher and chief backer, Markos Kounalakis — led her to sign on as publisher, with Leonard providing funding as Ms. Straus developed a new business model.
"It's not an exaggeration to say they saved the Monthly," said the magazine's editor in chief, Paul Glastris.
Ms. Straus, he said, found reliable financial backers in charitable organizations such as the Lumina Foundation, an education group that backed reporting efforts including the magazine's annual rankings of colleges that contribute to the public good. The magazine is "probably as financially solid as we've ever been," Glastris said.
Diane Ellen Straus was born in Manhattan on Oct. 23, 1951. A great-grandfather co-owned the Macy's department store chain, and Ms. Straus's father, R. Peter Straus, ran the Voice of America under President Jimmy Carter. Her mother, the former Ellen Sulzberger, founded Call for Action, considered the first national telephone help line, and was a cousin of former New York Times publisher Arthur Ochs Sulzberger.
A young Diane split her childhood between New York, Geneva and Washington, where she graduated from Sidwell Friends School. She was among the first women to graduate from Yale College — the university previously had admitted women only to its graduate schools — and according to the Platform Tennis Hall of Fame she founded and captained Yale's women's varsity tennis team.
She received a bachelor's degree in psychology in 1973 and worked as an editor at New York magazine and the Village Voice before becoming publisher of the Cranford Citizen and Chronicle, a New Jersey newspaper owned by her family.
A marriage to Carll Tucker III ended in divorce. Survivors include a companion, John Curtis of Washington; three children, Peter Tucker of Washington, Rebecca Tucker of Warwick, N.Y., and David Tucker of Bradford, Vt.; two sisters; a brother; and two grandchildren.
After being widowed, Ms. Straus's father married the mother of Monica Lewinsky, the White House intern whose relationship with President Bill Clinton spurred his impeachment proceedings.
"Monica is a bright, engaging and attractive young woman,'' Ms. Straus wrote in a 1998 Westchester Wag column, amid the furor surrounding her new stepsister. "Who hasn't made mistakes in their twenties?"
Ms. Straus's involvement with politics was late-blooming but deeply felt, friends said.
When Barack Obama was elected president in 2008, Leonard recalled, Ms. Straus "felt that while it's terrific that this bright and shining new star is being elected president, we need to be the loyal opposition, calling out and looking for better solutions in government, making government better, looking for new policy options beyond the rubber stamp of liberalism."
Correction: A previous version of this obituary incorrectly referred to Diane Straus's relationship to Monica Lewinsky. She was a stepsister, not a sister-in-law. The story has been updated.