Diane Straus, the publisher of two liberal policy magazines who was also a championship platform tennis player, died on Wednesday at her home in Washington. She was 66.

Her sister Jeanne Straus said the cause was cancer.

Diane Straus had been president and publisher of The American Prospect when she joined Washington Monthly in 2008, nearly 40 years after it was founded by Charles Peters.

At the time, the magazine was in danger of going out of business: Markos Kounalakis, Ms. Straus’ immediate predecessor, had provided the magazine with financing but had moved on.

Ms. Straus brought in new revenue by reaching out to foundations. And with funding from Jeffrey Leonard, a private equity manager who had left the board of The American Prospect to become chairman of Washington Monthly, the magazine survived, though it has reduced its frequency to five issues a year.

“Diane didn’t want to pitch ideology,’’ Leonard said in a telephone interview. “She wanted the foundations to be sold on independent journalism. Let the facts take us where the facts go.’’

Paul Glastris, the editor in chief, said Ms. Straus had been a staunch guardian of the magazine’s independence. “She had a passionate belief in the power of small magazines to make a difference,’’ Glastris said.

The magazine, which is a nonprofit, has continued to rely on foundations and other donors. Last year, it began an online project, Successes of Philanthropy, which is sponsored by foundations and other donors.

“A decade ago, foundations didn’t want to interfere in the market,’’ Ms. Straus once told The Chronicle of Philanthropy. But in recent years, she added, they decided “that they need to for serious independent journalism to survive.’’

Diane Ellen Straus was born in Manhattan on Oct. 23, 1951. Her father, R. Peter Straus, built a small empire of radio stations in New York state that included WMCA, which moved from a Top 40 music format to talk radio in 1970. He later augmented those holdings with weekly newspapers.

Peter Straus, who died in 2012, was also active in Democratic politics and served as director of the Voice of America in the 1970s.

Diane Straus’ mother, the former Ellen Sulzberger, helped run WMCA and founded Call for Action, the nation’s first telephone help line for individuals trying to solve problems they had encountered with government officials, corporations, and landlords. She was a cousin of Arthur Ochs Sulzberger, the former publisher of The New York Times.

While attending Yale, where she studied psychology and sociology, Ms. Straus started the university’s first women’s varsity tennis team and was its captain. She was in Yale’s first class of women to graduate, in 1973.

After college, she held editing jobs at New York magazine and The Village Voice before being named publisher of one of her family’s newspapers, The Cranford Citizen and Chronicle in New Jersey.

After taking a break to run a catering business, she became publisher of Trader Publications, a company run by her husband at the time, Carll Tucker III.

Ms. Straus returned to the print media world in 2005 as president and publisher of The American Prospect, where she stayed for three years before joining Washington Monthly.

Ms. Straus balanced publishing work with amateur platform tennis, which is played on an aluminum deck about one-third the size of a traditional tennis court. Twelve-foot-high fencing that surrounds the court allows the ball to be played off the walls.

Ms. Straus won more than two dozen titles, including two this year.

“She was determined and full of grit,’’ Robin Rich Fulton, one of her playing partners, said in a telephone interview. “She had willpower and a forehand that was out of this world, which set me up to close out the point.

“Her only weakness,’’ she added, “was her serve. She’d toss the ball so high that you could read a chapter of ‘Gone With the Wind’ before it came down.’’

Ms. Straus was inducted into the Platform Tennis Museum and Hall of Fame in Scarsdale, N.Y., in 2004.

That year she took a hiatus from her job as group publisher of Manhattan Media to work for Howard Dean, the former Vermont governor who was seeking the Democratic nomination for president.

In addition to her sister Jeanne, Ms. Straus leaves her companion, John Curtis; her daughter, Rebecca Tucker; her sons, Peter and David; two granddaughters; another sister, Katherine Straus; and a brother, Eric. Her marriage to Tucker ended in divorce.