Katharine Weymouth, director of advertising sales at The Washington Post Co. and niece of chairman and chief executive Donald E. Graham, will become vice president of newspaper advertising on Jan. 1, the company announced yesterday.

Weymouth, 38, will replace Susan O'Leary, who headed newspaper advertising for the $8.8 billion media and education company for the past four years and is leaving the company to move to Florida with her family.

A Stanford-educated lawyer, Weymouth has worked for The Post newspaper and Washingtonpost.Newsweek Interactive legal departments and most recently oversaw sales of classified and display recruitment ads for the newspaper and Web site. Recruitment ads suffered a significant decline in recent years, following the dot-com bust, but have been making some recent gains, jumping 21 percent at The Washington Post in the second quarter of this year, compared with the same period last year.

Running The Post Co.'s advertising "is a big assignment with all the pressure to go with it," said Washington Post President Stephen P. Hills. Advertising generates about 80 percent of The Post's revenue, with the rest coming from newspaper sales.

Weymouth is the granddaughter of the late Katharine Graham, at various times Post Co. president, chairman, chief executive and director from 1963 until her death in 2001. She is the daughter of Newsweek senior editor and socialite Lally Weymouth, Donald Graham's sister. Many in the company consider Katharine Weymouth a possible successor to her uncle.

"I know everyone says that," Weymouth said when asked about the possibility. "Honestly, it's not on my radar. I live day by day."

The only candidate considered for the job as advertising vice president, Weymouth takes over a division that, like those in other media companies, is still recovering from the 2001 advertising slump, the worst since World War II. At the end of 2001, Donald Graham told investors that Post ad revenue was down 13 percent from the previous year. In the second quarter of this year, advertising revenue at The Washington Post inched up 1 percent over the comparable period last year.

Newspapers have lost advertising to other media, as well, such as television, direct marketing and the Internet. But even though The Post continues to lose circulation (daily sales as of the second quarter of this year averaged 721,000 copies, down from 745,000 in the same period of 2003 and 759,900 in the second quarter of 2002), the paper's high level of penetration in the Washington market makes it a key advertising buy, Weymouth said.

"The paper still works," she said. "It's still not cheap to put an ad in The Post. Advertisers are not giving us money as a favor."

Weymouth is following the career track of her uncle. Before becoming publisher of The Post in 1979, Donald Graham held a number of jobs within the paper and company, including running the sports department for a year.

Weymouth said she has no plans to run the sports department, though she said that if she enters senior management of The Post Co. some day, she should have a newsroom job.

"If they'd have me," she said. "It's the area of the paper I know the least about."

Weymouth's lineage may give her the inside track to the top of The Post Co., but not a free pass if she does not excel, she said.

"This is a publicly traded company," she said. "Don would be the first to say, 'We love you, but this isn't working out.' "

Though Post Co. stock trades on Wall Street, voting shares are controlled by the Graham family, which has managed it through familial succession. Katharine Graham's father, Eugene Meyer, bought the newspaper at a bankruptcy auction in 1933 for $825,000.

Katharine Meyer married Philip Graham, who took over the paper upon Eugene Meyer's death in 1959. When Philip Graham died four years later, Katharine Graham became Post Co. president.

The line of succession is similar, if not as long-running, as that of the New York Times Co.'s controlling family. Times Co. Chairman Arthur O. Sulzberger Jr. is the great-grandson of Adolph Ochs, who acquired controlling interest of the Times in 1896 for $75,000.

In addition to The Washington Post newspaper, The Post Co. owns Kaplan Inc. educational company, Newsweek magazine, six television stations, a number of smaller newspapers including the Everett (Wash.) Herald, washingtonpost.com, and Cable One Inc., a cable company with more than 700,000 subscribers chiefly throughout the South and Plains states.